金属材料組織観察のための透過電子顕微鏡技法の開発と応用

電子線トモグラフィーによる格子欠陥の３次元可視化

高傾斜３軸試料ホルダーとその応用

3D Visualization of Dislocation Arrangements in Austenitic Stainless Steel with Dual-Axis STEM Tomography

オーステナイト系ステンレス鋼における全転位の３次元可視化

応力発光材料SrAl2O4:Eu2+における双晶界面の高分解能電子顕微鏡観察

SrAl2O4系応力発光材料に導入された面欠陥の透過型電子顕微鏡観察

EDS Analysis and Electron Tomography of New Precipitates on Lath Boundaries in 10Cr Ferritic Heat-Resistant Steel with V

V添加高強度耐熱鋼におけるラス境界析出物のEDS分析と3次元形態観察

Hybrid Electron Tomography Observation of Phase Separation in Ni-Al-Ti Superalloy

Ni-Al-Ti合金におけるγ’析出粒子の相分離組織の３次元TEM解析（Three-dimensional TEM analysis of phase separation of γ' particles in Ni-Al-Ti alloy）

The sleeping woman in the woods

Tomographic Dark-Field TEM Observation of Ordered Precipitates in Ni-Mo Alloy

暗視野TEMトモグラフィーによる合金中の規則バリアントの３次元形態観察

単結晶組成傾斜法と集束イオンビーム・マイクロサンプリング法によるAl-rich TiAl中の長周期規則構造の解析

高分解能電子顕微鏡像の定量評価による合金の短範囲規則構造の研究

Ni-Mo合金の短範囲−長範囲規則化過程の微視的機構に関する研究

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Physics Letters  

The realization of single crystal and bicrystal films of superconducting materials is of great interest because they allow the investigation of the intragrain performance as well as the understanding of potential limitations in the grain boundary transparency. For many years, the realization of a high-quality (Ba,K)Fe2As2 film has been challenging. Here, the realization of (Ba,K)Fe2As2 epitaxial thin films on single crystal SrTiO3(001) and [001]-tilt-type SrTiO3 bicrystal substrates with high superconducting properties is demonstrated. The epitaxial growth of (Ba,K)Fe2As2 was enabled by implementing an undoped BaFe2As2 buffer layer between the SrTiO3 substrate and (Ba,K)Fe2As2 film. The film exhibits a high Tc of 38.0 K and an extremely high Jc of 14.3 MA/cm2 at 4.2 K. Artificial grain boundaries of (Ba,K)Fe2As2 were also successfully achieved on bicrystals with misorientation angles up to 36.8° by the same preparation methods. The artificial grain boundaries exhibited an identical Tc of 38.0 K and an excellent transfer of the grain orientation from the bicrystal substrates with high crystallinity comparable to that of the high-quality Ba(Fe,Co)2As2 films. This enables the investigation of the intrinsic (Ba,K)Fe2As2 grain boundary nature, which will clarify its potential for superconducting applications, like Josephson junctions, wires, and magnets.

DOI： 10.1063/5.0233645

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Materialia  

Experimental observation methods for understanding industrially important solid-state sintering are essential for the development of new materials and devices. To experimentally characterize solid-state sintering, the limitations posed by the complexity of target materials, experimental equipment, and observation conditions must be overcome. Therefore, hybrid techniques for predicting sintering behavior based on experimental datasets and physics-based simulation models are highly sought after. Herein, we propose a new technique for combining a physics-based model and experimental observation results from solid-state sintering using a nonsequential Bayesian data assimilation (DA) method. The proposed technique assimilates experimental data—obtained using in situ electron tomography/scanning transmission electron microscopy—into the corresponding phase-field (PF) model to enable high-fidelity PF simulations by estimating multiple material parameters included in the PF model. This study demonstrates the inverse estimation of seven parameters, including temperature-dependent diffusion coefficients, from the time-series information on the morphology of sintered nanoparticles observed in situ. The estimated parameters provide the high-fidelity PF simulation to capture the observed solid-state sintering of copper nanoparticles. Thus, this study contributes to the construction of digital twins for solid-state sintering based on DA-integrated PF simulations and in situ observation datasets and deepens our understanding of the sintering process.

DOI： 10.1016/j.actamat.2024.120251

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出版者・発行元：Meteoritics and Planetary Science  

The surface morphology of regolith grains from the C-type asteroid Ryugu was studied in search of evidence of impact events on the asteroid. Scanning electron microscopy revealed that ~8% of C0105-042 Ryugu grains have a smooth surface on one side of the grains. One of these grains has striated linear grooves (striations) on its smooth surface. Transmission electron microscopy of the grain showed that a porous fine-grained Mg-Fe phyllosilicate assemblage, which is the main component of Ryugu grains, is compacted near the smooth surface. The smooth surface with striations closely resembles a slickenside, a characteristic texture found in terrestrial fault rocks formed by shear deformation. There is no evidence of melting/decomposition in the Mg-Fe phyllosilicates near the smooth surface, indicating that the shear heating temperature is less than ~1100 K. Assuming that the average length of the striations corresponds to the minimum displacement of the micro-fault, the shock pressure recorded in the C0105-042 Ryugu grain is estimated to be <~4.5 GPa by a fault mechanics calculation. The shock pressures of C0105-042, together with those of C0014 (~2 GPa) and C0055 (>~3.9 GPa) in previous studies suggest that the impact velocities recorded in these grains are < ~0.89–1.63 km s−1. Based on the impact velocities, these grains may record an impact event that occurred when asteroid Ryugu was in the orbit in Main Belt.

DOI： 10.1111/maps.14271

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記述言語：日本語   出版者・発行元：公益社団法人 日本顕微鏡学会  

<p>厚い試料の内部を可視化するのに，走査型透過型電子顕微鏡法（STEM）は結像レンズ系の色収差によって解像度が制限される透過型電子顕微鏡法と比べて優れている．そのため，走査型透過型電子顕微鏡法（STEM）は電子線トモグラフィーによる三次元構造解析にしばしば用いられる．しかし，特にフレームあたりミリ秒オーダーまたはそれ以上の高速イメージングを追求する場合，STEMの画質はノイズやアーチファクトによって顕著に劣化する．本稿では深層学習に基づくデノイズが高速STEM撮像に有効であること，また高速STEMトモグラフィーに応用できることを報告する．高速STEMトモグラフィーでは，わずか5秒の連続傾斜像収録で厚さ300 nmの鉄鋼試料からでも三次元転位配置が十分な精度で求まる．液体セルを含む比較的厚い媒質中の試料のその場観察またはオペランド観察に応用できると期待される．</p>

DOI： 10.11410/kenbikyo.59.2_52

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：NPG Asia Materials  

Superconducting magnets based on high-temperature superconductors (HTSs) have become critical components in cutting-edge technologies such as advanced medical applications. In HTSs, weak links of superconductivity are inevitable at high-angle grain boundaries (GBs). Thus, two adjacent grains should be crystallographically aligned within the critical angle (θc), for which the intergrain critical current density (Jc) starts to decrease exponentially. The θc of several iron-based superconductors (IBSs) is larger than that of cuprates. However, the decreases in both θc and intergrain Jc under magnetic fields for IBSs are still substantial, hampering their applications in polycrystalline forms. Here, we report that potassium-doped BaFe2As2 (Ba122:K) exhibits superior GB performance to that of previously reported IBSs. A transport Jc of over 0.1 MA/cm2 across [001]-tilt GBs with misorientation angles up to θGB = 24° was recorded even at 28 K, which is a required level for practical applications. Additionally, even in an applied magnetic field, θc was unaltered, and the decay of the intergrain Jc was small. Our results highlight the exceptional potential of Ba122:K for polycrystalline applications and pave the way for next-generation superconducting magnets.

DOI： 10.1038/s41427-024-00561-9

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その他リンク： https://www.nature.com/articles/s41427-024-00561-9

掲載種別：研究論文（学術雑誌）   出版者・発行元：Meteoritics and Planetary Science  

Samples were recently collected from the carbonaceous asteroid (162173) Ryugu, by the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission. They resemble CI chondrites material, thus showing clear evidence of extensive aqueous alteration attested by the widespread presence of a mixture of serpentine and saponite. We present here a scanning transmission electron microscopy study of the Ryugu dominant lithology of the phyllosilicate matrix at the nanometer scale, which we compare with that of the Orgueil CI chondrite. In both objects, the phyllosilicates are of comparable nature and texture, consisting of a mixture of small-sized crystallites of serpentine and saponite. At the micrometer scale or less, the texture is an alternation of fine and coarse domains. The fine-grained regions are dominated by saponite. In Ryugu, they enclose numerous Fe,Ni nanosulfides, whereas in Orgueil, S- and Ni-rich ferrihydrite is abundant. The coarse-grained regions contain more serpentine and no or little Fe,Ni sulfides or ferrihydrite. Scanning transmission x-ray microscopy at the Fe-L3 edge also reveals that iron valency of phyllosilicates is higher and more homogeneous in Orgueil (~70% Fe3+) than in Ryugu (<50% Fe3+). We interpret the observed textures as being mostly a consequence of aqueous alteration, likely resulting from the replacement by phyllosilicates of submicrometric components, initially agglomerated by a primary accretion. The fine-grained domains may result from the replacement of GEMS (GEMS—glass with embedded metal and sulfides) objects or from other types of nanometric assemblages of silicate and Fe-based nanophases. On the other hand, the coarse-grained regions may correspond to the replacement of anhydrous crystalline silicates of the olivine and pyroxene type. The major difference is the presence of Fe,Ni sulfides in Ryugu and of ferrihydrite and higher iron valency of phyllosilicates in Orgueil. This might be due to long-term terrestrial weathering that would have destabilized the nanosulfides. We also explore an alternative scenario involving more oxidizing hydrothermal conditions on the Orgueil parent body.

DOI： 10.1111/maps.14101

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Shape Memory and Superelasticity  

The effect of hydrogen charging duration on the transformation behavior, microstructural evolution, and dynamic microstructural changes associated with thermoelastic martensitic transformation in Ti–Ni shape memory alloy was investigated. Compared with the uncharged specimen, the martensitic transformation start (Ms) and reverse transformation finish (Af) temperatures increased with charging time, whereas the martensitic transformation finish and reverse transformation start temperatures remained almost unchanged. In situ SEM results were consistent with these behaviors. Upon cooling, the transformation progressed from the center to the surface in charged specimens, indicating a higher transformation temperature in the center than the surface. The latent heat of transformation decreased with increasing charging time, quantitatively attributed to an untransformed region consisting of hydrogen-induced martensite and a hydrogen-affected layer. The hydrostatic effect from those layers on the interior B2 phase was proposed as the origin of the increased Ms and Af temperatures.

DOI： 10.1007/s40830-024-00495-9

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その他リンク： https://link.springer.com/article/10.1007/s40830-024-00495-9/fulltext.html

出版者・発行元：Meteoritics and Planetary Science  

Regolith samples returned from asteroid 162173 Ryugu by the Hayabusa2 mission provide direct means to study how space weathering operates on the surfaces of hydrous asteroids. The mechanisms of space weathering, its effects on mineral surfaces, and the characteristic time scales on which alteration occurs are central to understanding the spectroscopic properties and the taxonomy of asteroids in the solar system. Here, we investigate the behavior of the iron monosulfides mineral pyrrhotite (Fe1−xS) at the earliest stages of space weathering. Using electron microscopy methods, we identified a partially exposed pyrrhotite crystal that morphologically shows evidence for mass loss due to exposure to solar wind ion irradiation. We find that crystallographic changes to the pyrrhotite can be related to sulfur loss from its space-exposed surface and the diffusive redistribution of resulting excess iron into the interior of the crystal. Diffusion profiles allow us to estimate an order of magnitude of the exposure time of a few thousand years consistent with previous estimates of space exposure. During this interval, the adjacent phyllosilicates did not acquire discernable damage, suggesting that they are less susceptible to alteration by ion irradiation than pyrrhotite.

DOI： 10.1111/maps.14176

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Microscopy  

In-situ observation has expanded the application of transmission electron microscopy (TEM) and has made a significant contribution to materials research and development for energy, biomedical, quantum, etc. Recent technological developments related to in-situ TEM have empowered the incorporation of three-dimensional observation, which was previously considered incompatible. In this review article, we take up heating as the most commonly used external stimulus for in-situ TEM observation and overview recent in-situ TEM studies. Then, we focus on the electron tomography (ET) and in-situ heating combined observation by introducing the authors’ recent research as an example. Assuming that in-situ heating observation is expanded from two dimensions to three dimensions using a conventional TEM apparatus and a commercially available in-situ heating specimen holder, the following in-situ heating-and-ET observation procedure is proposed: (i) use a rapid heating-and-cooling function of a micro-electro-mechanical system holder; (ii) heat and cool the specimen intermittently and (iii) acquire a tilt-series dataset when the specimen heating is stopped. This procedure is not too technically challenging and can have a wide range of applications. Essential technical points for a successful 4D (space and time) observation will be discussed through reviewing the authors’ example application.

DOI： 10.1093/jmicro/dfae008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本金属学会  

Microstructure and its evolution of solute-enriched stacking faults (SESFs) in kink-deformed Mg–Zn–Y alloys have been investigated by scanning transmission electron microscopy (STEM). Mass-thickness contrast in annular dark-field (ADF) STEM images and diffraction contrast in weak-beam dark-field (WBDF) STEM images visualized locations of solute-enriched regions and dislocations, respectively. Most of the SESFs are located at or near kink boundaries, and a variety of arrangements and morphology of the SESFs are followed by dislocations with the c component of α-Mg matrix and small-angle lattice rotations along the c-axis as well as the a-b axes. As notable microstructural features of the SESFs, rectangular-shaped and step-shaped arrangements of the SESFs, observed respectively before and after a heat treatment at 573 K for 168h, were observed in detail, and their formation processes were discussed.

DOI： 10.2320/matertrans.mt-m2023186

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Acta Materialia  

In this study, the microstructure of polycrystalline Co-doped BaFe2As2 superconducting bulks was comprehensively analyzed. The synthesis process involved ball milling and subsequent spark plasma sintering (SPS). A strong correlation between the microstructure and synthesis conditions was observed. Specifically, when mechanochemical synthesis of raw metal powders was carried out at a ball milling energy (EBM) of 100 MJ/kg, the resulting Co-BaFe2As2 bulk contained nanograins with a high density of planar defects and exhibited a high critical current density (Jc) under both magnetic and self-fields. The findings suggest that planar defects are one of the influential factors on the superconducting properties. Atomic-resolution microstructural characterization revealed that the planar defects are parallel to (001) and exhibit distinctive atomic arrangements. Atomic-resolution elemental mappings displayed a remarkable barium concentration in planar defects and grain boundaries compared to the BaFe2As2 matrix. Local strain fields were also observed around planar defects, especially near their edges. These nanoscale strain fields could be considered as volumetric pinning centers, and effectively pin flux vortices in the random crystal orientation, thereby increasing Jc in the Fe-based superconducting bulk. Additionally, an extended investigation was performed to include a K-doped BaFe2As2 bulk that exhibits similar planar defects. Based on the results of the microstructural analysis, speculations were mode on the evolution process of the microstructure during the preparation of BaFe2As2 bulks.

DOI： 10.1016/j.actamat.2024.119648

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nature Astronomy  

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized.

DOI： 10.1038/s41550-023-02137-z

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記述言語：英語   出版者・発行元：Springer Nature  

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized.

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Meteoritics and Planetary Science  

The Hayabusa2 mission from the Japan Aerospace Exploration Agency (JAXA) returned to the Earth samples of carbonaceous asteroid (162173) Ryugu. This mission offers a unique opportunity to investigate in the laboratory samples from a C-type asteroid, without physical or chemical alteration by the terrestrial atmosphere. Here, we report on an investigation of the mineralogy and the organo-chemistry of Hayabusa2 samples using a combination of micro- and nano-infrared spectroscopy. Particles investigated with conventional FTIR spectroscopy have spectra dominated by phyllosilicate-related absorption, as observed for samples of CI-chondrites, selected ungrouped carbonaceous chondrites, and selected hydrated micrometeorites. Ryugu samples show smaller sulfate-related absorption than CI-chondrites. Our samples that were only briefly exposed to the Earth atmosphere show absorptions related to molecular water, revealing fast terrestrial contamination of the spectral signature at 3 μm. Overall, our FTIR data are in agreement with other work done on Ryugu samples, revealing a low degree of mineralogical variability across Ryugu samples. AFM-IR mapping of the grains shows the presence of a micrometer-sized organic globule in one of our analyzed grains. The AFM-IR spectra obtained on this globule are similar to IR spectra obtained on IOM suggesting that it is constituted of refractory organic matter. This globule may host silicate in its interior, with a different mineralogy than bulk Ryugu phyllosilicate. The shape, presence of peculiar silicate, and the nature of organic constituting the globule point toward a pre-accretionary origin of this globule and that at least part of Ryugu organics were inherited from the protosolar nebulae or the interstellar media. Altogether, our results show the similarities between Ryugu samples and CI chondrites.

DOI： 10.1111/maps.14122

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Meteoritics and Planetary Science  

Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate-rich matrix with four-dimensional scanning transmission electron microscopy (4D-STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni-bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d-spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d-spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d-spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry.

DOI： 10.1111/maps.14124

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Applied Glass Science  

Herein, the crystallization behavior of a Li2O–Al2O3–SiO2 (LAS) glass system with the addition of ZrO2 and SnO2 as nucleating agents was investigated using X-ray diffraction, differential scanning calorimetry, four-dimensional scanning transmission electron microscopy, and X-ray absorption fine-structure measurements. At lower heat-treatment temperatures, the addition of ZrO2 and SnO2 afforded a ZrSnO4 solid solution (SS), whereas at higher heat-treatment temperatures, the ZrSnO4 SS decomposed, affording tetragonal ZrO2 and tetragonal SnO2. LAS-based crystalline phases, such as β-quartz and β-spodumene phases SS, were formed after the formation of the ZrSnO4 SS. ZrSnO4 SS particles a few nanometers in size were present in contact with the β-quartz SS particles a few dozen nanometers in size. This suggests that the ZrSnO4 SS served as a crystal nucleus for the β-quartz SS, promoting its growth.

DOI： 10.1111/ijag.16644

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Meteoritics and Planetary Science  

Abstract

Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low‐temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non‐globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy‐dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C₁₀₀N₃O₉S₁ and C₁₀₀N₃O₇S₁, respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CH_n), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO₃) absorption, comparable to prior observations of clay‐bound organic matter in CI meteorites.

DOI： 10.1111/maps.14128

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記述言語：日本語   出版者・発行元：日本結晶成長学会  

<p>  Metal nanoparticles undertake sintering at a lower temperature compared to their bulk counterparts, attracting great attention in industrial applications such as printed electronics. Since nanoparticles are easy to aggregate, the three-dimensional (3D) visualization of their sintering process plays a vital role in quantifying the morphological changes during heating. However, the nanoparticles are sensitive to surface contamination, resulting in poor affinity to the 3D visualization with conventional electron beam intensity because the visualization technique requires a long beam exposure time, potentially making beam induced contamination significant. In this paper, we demonstrate our developed 3D observation scheme, including advanced image processing techniques. A sample transfer system, which enables to prevent nanoparticles from being exposed to air, and an ultra-low-electron dose observation protocol prevents surface contamination during the observation. The low-signal-to-noise ratio of acquired images is compensated by the advanced image processing techniques. The obtained 3D images of nanoparticles enable to measure the neck growth and variation of particle distance in 3D during the sintering in a quantitative way.</p>

DOI： 10.19009/jjacg.51-1-03

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Meteoritics and Planetary Science  

Samples returned from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 mission revealed that Ryugu is composed of materials consistent with CI chondrites and some types of space weathering. We report detailed mineralogy of the fine-grained Ryugu samples allocated to our “Sand” team and report additional space weathering features found on the grains. The dominant mineralogy is composed of a fine-grained mixture of Mg-rich saponite and serpentine, magnetite, pyrrhotite, pentlandite, dolomite, and Fe-bearing magnesite. These grains have mineralogy comparable to that of CI chondrites, showing severe aqueous alteration but lacking ferrihydrite and sulfate. These results are similar to previous works on large Ryugu grains. In addition to the major minerals, we also find many minerals that are rare or have not been reported among CI chondrites. Accessory minerals identified are hydroxyapatite, Mg-Na phosphate, olivine, low-Ca pyroxene, Mg-Al spinel, chromite, manganochromite, eskolaite, ilmenite, cubanite, polydymite, transjordanite, schreibersite, calcite, moissanite, and poorly crystalline phyllosilicate. We also show scanning transmission electron microscope and scanning electron microscope compositional maps and images of some space-weathered grains and severely heated and melted grains. Although our mineralogical results are consistent with that of millimeter-sized grains, the fine-grained fraction is best suited to investigate impact-induced space weathering.

DOI： 10.1111/maps.14093

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Alloys and Compounds  

It has been reported that functional and mechanical properties of Ti-Ni shape memory alloys could be degraded by hydrogen absorption. Many studies have indicated the formation of a hardened layer on the surface in hydrogen-absorbed Ti-Ni alloys. However, the underlying microstructural features and their impact on the functional and mechanical properties remain unclear. In the present study, ex situ and in situ electron microscopy characterizations of the high-hardness layer in a hydrogen-charged Ti-Ni alloy were performed for the first time. Electron diffraction and atomic resolution imaging revealed that the hardened layers have an orthorhombic structure with a four-layer stacking sequence and a martensitic-like crystallographic nature such as lattice correspondence including 12 variants of the orthorhombic phase against each orientation of the parent cubic (B2) phase. In situ and ex situ observations in an electron microscope confirmed that the orthorhombic phase undergoes athermal transformation upon cooling and stress- and/or strain-induced transformation upon deformation, which further characterizes the martensitic-like nature of this phase. The effect of hydrogen on the original phase transformation from the cubic (B2) to the monoclinic (B19′) structure is also discussed.

DOI： 10.1016/j.jallcom.2023.171470

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Luminescence  

Highly luminescent red emitting Zn2+ modified Gd2O3:Eu3+, Li + nanophosphors with superior colour purity were prepared by the organic mediated solvothermal combustion of metal-citrates in diethylene glycol. Structure, morphology, spectroscopic and luminescence dynamics of the nanophosphors were found to be sensitive to Zn2+ concentration. Simultaneous incorporation by Zn2+ and Li+ ions in Gd2O3:Eu3+ resulted in better emission features and improved photophysical radiative properties. Enhanced photoemission has resulted from the cooperative and combined roles caused by Li+ and Zn2+ ions, improvement of crystallinity, modifications of the crystal field and reduced symmetry around Eu3+ ions in Gd2O3. Photoemission intensity of the optimal zinc compensated phosphor with composition Gd1.71Eu0.1Li0.15Zn0.04O3 was found to be 1.82 times that of Gd1.75Eu0.1Li0.15O3 and it exhibited a lifetime of 1.467 ms with the highest colour purity of 97.06 %. Luminescence decay profiles of all the synthesized phosphors were found to follow single exponential behaviour. Judd-Ofelt analysis revealed that the emission intensity parameters were found to be optimum for Gd1.71Eu0.1Li0.15Zn0.04O3 phosphor, indicating the highest asymmetry of local environment around Eu3+ ions in this material. Better radiative and Judd-Ofelt intensity parameters obtained indicate that this highly luminescent red emitting phosphor can act as a promising material for high resolution phosphor coated displays, deep UV excited phosphor converted LEDs and for developing defence security inks.

DOI： 10.1016/j.jlumin.2023.120150

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Applied Superconductivity  

For obtaining microscopic knowledge toward a fabrication process of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi,Pb-2223) single-phase material, we fabricated a multilayered film on a SrTiO3(001) substrate by a sputtering method using (Bi,Pb)2Sr2CaCu2Oy (Bi,Pb-2212) and Pb-Ca-Cu-O targets alternately at 650 °C. The as-grown film was an epitaxially grown multilayered film consisting of Bi,Pb-2212 and Pb-Ca-Cu-O layers. Coarse grains of impurity phases were also formed within the multilayered film, and these impurity phases were difficult to eliminate even after heat treatments. After 10 h heat treatment at 840 °C with Bi,Pb-2223 pellets, the phase transition from Bi,Pb-2212 to Bi,Pb-2223 occurred in the multilayered film. The phase transition to Bi,Pb-2223 proceeded preferentially at the interface with the impurity phases and the Pb-Ca-Cu-O layers. These observation results suggest that the impurity phases promote three-dimensional atomic diffusion in the multilayered film to accelerate the phase transition to Bi,Pb-2223, as well as consume constituent elements, Ca, Cu and O. Even after the 100 h heat treatment at 840 °C with Bi,Pb-2223 pellets, the phase transition from Bi,Pb-2212 to Bi,Pb-2223 did not proceed completely, and the fraction of the Bi,Pb-2223 phase in the whole superconducting phases was ∼50&#37;. It is suggested that controlling the formation and microstructure of the impurity phases is a key to further increasing the fraction of the Bi,Pb-2223 phase.

DOI： 10.1109/TASC.2023.3259920

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of the American Ceramic Society  

It is known that the addition of Li2O to 33.3BaO-66.7SiO2 glass, whose composition is the same as BaSi2O5, promotes crystallization of BaSi2O5. In this study, in order to clarify the effect of a smaller amount of Li2O, xLi2O-(30-x)BaO-70SiO2[mol&#37;] (x = 0, 0.2, 0.5) glasses were prepared. The main crystalline phases in the heat treatments near the maximum crystallization peak temperature, were high-BaSi2O5 and low-BaSi2O5 which transformed from high-BaSi2O5. It is found that the introduction of only 0.2 mol&#37; and 0.5 mol&#37; Li2O significantly changes the crystallization behavior. In the composition without Li2O, only high-BaSi2O5 was formed after heat treatment even for 24 h. For compositions containing Li2O, low-BaSi2O5 was formed within 1 h of heat treatment. In these compositions, it is found that the addition of Li2O enhances phase separation in the early stage of heat treatment, resulting in the formation of Si-rich droplet phases and Ba-rich phases. The composition of the Ba rich glass phase would be close to the stoichiometric composition of BaSi2O5, suggesting a significant change in crystallization behavior.

DOI： 10.1111/jace.19099

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nanoscale  

The nanoscale characterization of thermally activated solid reactions plays a pivotal role in products manufactured by nanotechnology. Recently, in situ observation in transmission electron microscopy combined with electron tomography, namely four-dimensional observation for heat treatment of nanomaterials, has attracted great interest. However, because most nanomaterials are highly reactive, i.e., oxidation during transfer and electron beam irradiation would likely cause fatal artefacts; it is challenging to perform the artifact-free four-dimensional observation. Herein, we demonstrate our development of a novel in situ three-dimensional electron microscopy technique for thermally activated solid-state reaction processes in nanoparticles (NPs). The sintering behaviour of Cu NPs was successfully visualized and analyzed in four-dimensional space-time. An advanced image processing protocol and a newly designed state-of-the-art MEMS-based heating holder enable the implementation of considerably low electron dose imaging and prevent air exposure, which is of central importance in this type of observation. The total amount of electron dose for a single set of tilt-series images was reduced to 250 e− nm−2, which is the lowest level for inorganic materials electron tomography experiments. This study evaluated the sintering behaviour of Cu NPs in terms of variations in neck growth and particle distance. A negative correlation between the two parameters is shown, except for the particle pair bound by neighbouring NPs. The nanoscale characteristic sintering behavior of neck growth was also captured in this study.

DOI： 10.1039/D3NR00992K

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記述言語：その他   出版者・発行元：Superconductor Science and Technology  

Abstract

Since the discovery of Fe-based superconductors, a lot of effort has been devoted to growing single crystals and epitaxial thin films of them for fundamental studies and applied research of superconductivity. As a result, epitaxial thin films of the most of Fe-based superconductors have been realized. However, some of the materials, namely pristine and transition-metal-doped (Li,Fe)OHFeSe, hydrogen-doped LnFeAsO (Ln = Nd and Sm), Co-doped SmFeAsO, and K-doped BaFe₂As₂ have been available only in the form of single crystals due to, e.g. the difficulty in doping hydrogen, obtaining high-quality sintered bulks for the target used for pulsed laser deposition, and controlling volatile elements. By solving those issues, the aforementioned compounds have been successfully fabricated as epitaxial thin films in recent years. Unlike single crystals, transport critical current measurements are relatively easy on thin films, which can help evaluate the application potential. In this article, we give an overview over the growth methods for epitaxial thin films of those compounds, followed by their physical properties, especially focusing on electrical transport.

DOI： 10.1088/1361-6668/acccb2

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-6668/acccb2/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geochimica et Cosmochimica Acta  

We have investigated several particles collected during each of two touchdowns of the Hayabusa2 spacecraft at the surface of the C-type asteroid 162173 Ryugu using various electron microscope techniques. Our detailed transmission electron microscopy study shows the presence of magnetite with various morphologies coexisting in close proximity. This is characteristic of CI chondrite-like materials and consistent with the mineral assemblages and compositions in the Ryugu parent body. We describe the microstructural characteristics of magnetite with different morphologies, which could have resulted from the chemical conditions (growth vs. diffusion rate) during their formation. Furthermore, we describe the presence of magnetites with a spherulitic structure composed of individual radiating fibers that are characterized by pervasive, homogeneously distributed euhedral to subhedral pores that have not been described in previous chondrite studies. This particular spherulitic structure is consistent with crystallization under nonequilibrium conditions. Additionally, the presence of a high density of defects within the magnetite fibers, the high surface/volume ratio of this morphology, and the presence of amorphous materials in several pores and at the edges of the acicular fibers further support their formation under nonequilibrium conditions. We suggest that the growth processes that lead to this structure result from the solution reaching a supersaturated state, resulting in an adjustment to a lower free energy condition via nucleation and rapid growth.

DOI： 10.1016/j.gca.2023.02.003

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Microscopy  

Electron tomography (ET) is a powerful tool for elucidating the properties and functionalities of materials. The innovative development of aberration-corrected electron microscopy in the early 21st century and the remarkable progress in the development of detectors, equipment and devices related to ET have resulted in substantial improvements in resolution. However, not only advances in hardware but also remarkable developments in reconstruction algorithms and related three-dimensional (3D) analysis methods have contributed to the resolution improvements. ET has its own problems, including the missing-wedge problem due to the limited tilt-angle range and the need to acquire numerous specimen-tilt images, the latter of which is time-consuming and can potentially damage the specimen. This review paper aims to (i) describe the established basic theories and definitions regarding 3D resolution of ET and practical 3D resolution measurement methods, (ii) discuss various reconstruction algorithms that effectively overcome the aforementioned problems and (iii) describe recent progress in the core of ET applications in materials science with respect to atomic ET, analytical ET and in-situ ET. The aforementioned ET problems have been addressed with each method developed in each field of application. Notably, in terms of aim (ii), recently developed reconstruction algorithms can reduce the number of projection images (specimen-tilt images) needed to attain a certain resolution without violating the Nyquist criterion. This approach is interpreted as a novel non-linear sampling theorem.

DOI： 10.1093/jmicro/dfac071

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Nature  

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

DOI： 10.1038/s41550-022-01841-6

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記述言語：英語  

DOI： 10.1073/pnas.2203628119

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Superconductor Science and Technology  

Abstract

Molecular beam epitaxy of K-doped Ba122 (Ba_1−xK_xFe₂As₂) superconductor was realized on an MgO substrate. Microstructural observation revealed that the undoped Ba122 served as a perfect buffer layer for epitaxial growth of the K-doped Ba122. The film exhibited a high critical temperature of 39.8 K and a high critical current density of 3.9 MA cm⁻² at 4 K. The successful growth of epitaxial thin film will enable artificial single grain boundary on oxide bicrystal substrates and reveal the grain boundary transport nature of K-doped Ba122.

DOI： 10.1088/1361-6668/ac8025

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その他リンク： https://iopscience.iop.org/article/10.1088/1361-6668/ac8025/pdf

記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ultramicroscopy  

The sensitive coherent interference of electron waves arising from a specimen is useful for revealing subtle structural information in electron micrographs, which can be important for minimising dose and for rapid imaging. In general, dynamical diffraction is expected due to the useful strong interactions of electrons with matter, which can create phase contrast that violates the requisite Radon projection assumption for tomography. It is for these reasons that incoherent imaging modalities such as high angle annular dark field have been favoured to date in electron tomography of crystalline specimens, to access a monotonic relationship between specimen thickness and micrograph intensity. Here we use a geometric approach to track topological features that are robust to perturbation of the imaging conditions, to enable 3D reconstructions from electron microscope tilt series under imaging conditions that violate the Radon projection assumption, with an emphasis on phase contrast. Invoking a sparsity assumption, we demonstrate that topological features can be reliably tracked in 3D using a differential geometric form of stereoscopy, to circumvent departures from the projection approximation and reduce noise by effecting segmentation of interest points from the outset. We demonstrate this approach on a variety of different specimen and data types, from polyhedral nanoparticles, to steel dislocation networks, cryo-EM cellular structures and 3D diffuse diffraction of a relaxor ferroelectric.

DOI： 10.1016/j.ultramic.2022.113475

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記述言語：英語   出版者・発行元：一般社団法人 日本鉄鋼協会  

To quantitatively evaluate the three-dimensional lamellar curvature in pearlitic steel, the crystallographic orientation rotation of ferrite and cementite was analyzed using scanning electron microscopy and electron backscattering diffraction. In the hypereutectoid steel containing 0.92% C, 0.30% Mn, 0.20% Si, and 0.19% Cr, the ferrite-cementite interfaces in some colonies were confirmed to match well with those having frequently observed habit planes with the Pitsch-Petch orientation relationship. It was also confirmed that the ferrite and cementite near the ferrite-cementite interface rotated toward the same orientation to maintain the Pitsch-Petch orientation relationship and the habit plane. Based on the confirmation that the ferrite-cementite interface is well approximated by (010) plane of the adjacent cementite, the lamellae were revealed to have three-dimensional anisotropic curvature.

DOI： 10.2355/isijinternational.isijint-2021-194

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記述言語：日本語   出版者・発行元：公益社団法人 日本金属学会  

DOI： 10.2320/materia.61.84

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その他リンク： https://www.jstage.jst.go.jp/article/materia/61/2/61_84/_pdf

記述言語：英語  

記述言語：英語  

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記述言語：英語   出版者・発行元：エルゼビア・ジャパン(株)  

ヒアルロン酸の関節内注射後に、壊死性筋膜炎を発症した剖検例について報告した。症例は73歳女性で、肩関節周囲炎と変形性膝関節症による関節痛のため、クリニックで左肩と左膝にヒアルロン酸の関節内注射を受けていた。夫の証言では、帰宅後、PM10時頃はリビングでソファの近くで寝ていたが、翌朝AM10時頃、ソファの下で仰臥位で死んでいた。また、法医解剖では左肩と左膝に水疱と紅斑を伴った注射痕が認められ、左上腕部と左大腿部には筋組織の液化壊死が観察された。さらに、病理組織学検査では、左上腕部と左大腿部に多数の細菌クラスターを伴った重度の横紋筋融解症も認められ、細菌学的検査ではA群レンサ球菌が検出され、血液生化学検査では血中尿素窒素、クレアチニンおよびC反応性タンパク質の濃度上昇も認められた。これらの所見から、死因は劇症型溶血性レンサ球菌感染症(STSS)と診断され、感染経路として、注射が適切に行われておらず、細菌の侵入経路となった可能性が示唆された。

記述言語：日本語   出版者・発行元：公益社団法人 低温工学・超電導学会 (旧 社団法人 低温工学協会)  

<p>MgB₂ compound is one of the low activation superconducting materials because the half-life time of the MgB₂ phase is much shorter than that of the Nb-based superconductors, such as Nb-Ti and Nb₃Sn. The natural boron powder as the boron source of the in-situ MgB₂ wire and bulk consists of two kinds of stable isotope materials, which are B-10 (¹⁰B:19.78 %) and B-11 (¹¹B: 80.22 %) isotopes. The ¹¹B isotope is a promising raw material for the further improvement of the neutron irradiation effect on the low activation MgB₂ wire. This study focused on the quality effect of the ¹¹B isotope raw powder on the superconducting properties of the ¹¹B isotope-originated MgB₂ (Mg¹¹B2) wire. We found that the nano-order particle size and the higher purification of the ¹¹B isotope raw powder would be efficient in the improvement of the superconducting properties of the low activation Mg¹¹B₂ wire.</p>

DOI： 10.2221/jcsj.57.31

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その他リンク： http://id.ndl.go.jp/bib/031955193

記述言語：英語   掲載種別：研究論文（学術雑誌）  

<title>Abstract</title>The most effective way to enhance the dissipation-free supercurrent in the presence of a magnetic field for type II superconductors is to introduce defects that act as artificial pinning centers (APCs) for vortices. For instance, the in-field critical current density of doped BaFe₂As₂ (Ba122), one of the most technologically important Fe-based superconductors, has been improved over the last decade by APCs created by ion irradiation. The technique of ion irradiation has been commonly implemented to determine the ultimate superconducting properties. However, this method is rather complicated and expensive. Here, we report a surprisingly high critical current density and strong pinning efficiency close to the crystallographic <italic>c</italic>-axis for a K-doped Ba122 epitaxial thin film without APCs, achieving performance comparable to ion-irradiated K-doped Ba122 single crystals. Microstructural analysis reveals that the film is composed of columnar grains with widths of approximately 30–60 nm. The grains are rotated around the <italic>b</italic>- (or <italic>a</italic>-) axis by 1.5° and around the <italic>c</italic>-axis by −1°, resulting in the formation of low-angle grain boundary networks. This study demonstrates that the upper limit of in-field properties reached in ion-irradiated K-doped Ba122 is achievable by grain boundary engineering, which is a simple and industrially scalable manner.

DOI： 10.1038/s41427-021-00337-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The recent realisations of hydrogen doped LnFeAsO (Ln = Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density Jc. The superconducting transition temperature Tc is comparable to NdFeAs(O,F). Transmission electron microscopy investigation supported that hydrogen is homogenously substituted for oxygen. A high self-field Jc of over 10 MA/cm2 was recorded at 5 K, which is likely to be caused by a short London penetration depth. The anisotropic Ginzburg–Landau scaling for the angle dependence of Jc yielded temperature-dependent scaling parameters γJ that decreased from 1.6 at 30 K to 1.3 at 5 K. This is opposite to the behaviour of NdFeAs(O,F). Additionally, γJ of NdFeAs(O,H) is smaller than that of NdFeAs(O,F). Our results indicate that heavily electron doping by means of hydrogen substitution for oxygen in LnFeAsO is highly beneficial for achieving high Jc with low anisotropy without compromising Tc, which is favourable for high-field magnet applications.

DOI： 10.1038/s41598-021-85216-3

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Scanning transmission electron microscopy (STEM) is suitable for visualizing the inside of a relatively thick specimen than the conventional transmission electron microscopy, whose resolution is limited by the chromatic aberration of image forming lenses, and thus, the STEM mode has been employed frequently for computed electron tomography based three-dimensional (3D) structural characterization and combined with analytical methods such as annular dark field imaging or spectroscopies. However, the image quality of STEM is severely suffered by noise or artifacts especially when rapid imaging, in the order of millisecond per frame or faster, is pursued. Here we demonstrate a deep-learning-assisted rapid STEM tomography, which visualizes 3D dislocation arrangement only within five-second acquisition of all the tilt-series images even in a 300 nm thick steel specimen. The developed method offers a new platform for various in situ or operando 3D microanalyses in which dealing with relatively thick specimens or covering media like liquid cells are required.

DOI： 10.1038/s41598-021-99914-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Lattice expansion and surface stress for tetragonal SnO2 nanorods and nanosheets were systematically investigated using lattice constants determined from in situ synchrotron radiation X-ray powder diffraction of hydrothermal synthesis. A particle size dependence of lattice constants a and c for the nanorods was identical to that for the nanosheets in the same size within experimental uncertainties. The fact suggests the lattice constants of SnO2 nanostructured materials only depend on the particle size parallel to the crystallographic axis. The average atomic volume of the nanorods and nanosheets linearly depends on the ratio of the particle surface area A to volume V in A/V < 0.5 nm(-1). The surface stress estimated in A/V < 0.5 nm(-1) was -1.7(2) N/m with a reasonable average atomic volume for bulk. Significant deviations from the linear line were observed in A/V > 0.5 nm(-1) for the nanorods and nanosheets. A boundary of expansion behavior was found to be the particle size of similar to 9 nm. The critical length of 9 nm has an effect on the study of their application for Li-ion batteries since SnO2 nanostructured materials with size from a few nanometers to tens of nanometers have been fabricated and investigated for anodes in lithium-ion batteries.

DOI： 10.1021/acsanm.1c02615

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The demand for affordable energy will continue to increase. On the other side, the utilization of fossil fuels is causing drastic changes to our climate forcing us to search for more sustainable sources of energy. Lignocellulosic biomass waste from palm oil industry in Malaysia is one of the most abundant and economically attractive sources of renewable energy. This can be utilized as the raw material for solid biofuel, i.e., Bio-Coke. Some efforts have been made to improve the quality of Bio-Coke in recent years. This study aims to determine the influence of biological pretreatment of oil palm empty fruit bunch (EFB) on its subsequent Bio-Coke characteristics. The results show after pretreatment, the fiber structure of EFB could be seen clearly and a looser connection between single fibers is observed. The pretreatment leads to the biologically pretreated Bio-Coke having higher apparent density and longer combustion duration than the Bio-Coke without pretreatment.

DOI： 10.1016/j.biteb.2021.100765

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This paper reports the nanoscale texture and microstructure of a high-performance NdFeAs(O,F) superconducting thin film grown by molecular beam epitaxy on a textured MgO/Y2O3/Hastelloy substrate. The NdFeAs(O,F) film forms a highly textured columnar grain structure by epitaxial growth on the MgO template. Although the film contains stacking faults along the ab-plane as well as grain boundaries perpendicular to the ab-plane, good superconducting properties are measured: a critical temperature, T-c, of 46 K and a self-field critical current density, J(c), of 2 x 10(6) A/cm(2) at 4.2 K. Automated crystal orientation mapping by scanning precession electron diffraction in transmission electron microscope is employed to analyze the misorientation angles between adjacent grains in a large ensemble (247 grains), and 99&#37; of the grain boundaries show in-plane misorientation angles (Delta gamma) less than the critical angle theta(c), which satisfies one of the necessary conditions for the high J(c). Comparing the columnar grain size distribution with the mean distance of the flux line lattice, the triple junctions of low-angle grain boundaries are found to be effective pinning centers, even at high temperatures (>= 35 K) and/or low magnetic fields.

DOI： 10.1021/acsaelm.1c00364

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The temperature dependence thermal conductivity of the indium-gallium-zinc oxide (IGZO) thin films was investigated with the differential three-omega method for the clear demonstration of nanocrystallinity. The thin films were deposited on an alumina (α-Al2O3) substrate by direct current (DC) magnetron sputtering at different oxygen partial pressures ([PO2] = 0&#37;, 10&#37;, and 65&#37;). Their thermal conductivities at room temperature were measured to be 1.65, 1.76, and 2.58 Wm−1K−1, respectively. The thermal conductivities decreased with an increase in the ambient measurement temperature. This thermal property is similar to that of crystalline materials. Electron microscopy observations revealed the presence of nanocrystals embedded in the amorphous matrix of the IGZO films. The typical size of the nanocrystals was approximately 2–5 nm with the lattice distance of about 0.24–0.26 nm. These experimental results indicate that the nanocrystalline microstructure controls the heat conduction in the IGZO films.

DOI： 10.3390/nano11061547

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In Y2O3 ceramics densified at 1000 °C by spark plasma sintering (SPS), non-uniform sintering behavior of grains and pores occurred for a heating rate of 20 °C/min. The sintered Y2O3 was translucent at the periphery but white and opaque at the center. According to microstructural analysis, the non-uniform sintering was caused by rapid grain growth and pore coarsening at the center. Under complicated electric and magnetic fields during SPS, an assumption of the movement of defects toward the center enables to explain the microstructural non-uniformity. For the non-uniform sintering behavior, spectroscopic analysis was used to investigate the introduced impurities (C, H, O) and by-products (carbonates). In the spectroscopic analysis, the peaks located at 2555, 2950, and 3560 cm11 (OH stretching band of H2O) were weakly detected for low heating rates but clearly detected for high heating rates. This is because H2O adsorbed to the initial Y2O3 powder was not sufficiently removed and was trapped during rapid densification at high heating rates. Due to the carbon-rich environment during SPS, carbonate was formed by the reaction of carbon with OH. Most carbons were detected as a CO peak, indicating that a reaction of carbon with OH occurred.

DOI： 10.2109/jcersj2.20173

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The iron-based superconductor Ba1-xKxFe2As2 is emerging as a key material for high magnetic field applications owing to the recent developments in superconducting wires and bulk permanent magnets. Epitaxial thin films play important roles in investigating and artificially tuning physical properties; nevertheless, the synthesis of Ba1-xKxFe2As2 epitaxial thin films remained challenging because of the high volatility of K. Herein, we report the successful growth of epitaxial Ba1-xKxFe2As2 thin films by molecular-beam epitaxy with employing a combination of fluoride substrates (CaF2, SrF2, and BaF2) and a low growth temperature (350-420 degrees C). Our epitaxial thin film grown on CaF2 showed sharp superconducting transition at an onset critical temperature of 36 K, slightly lower than bulk crystals by similar to 2 K due presumably to the strain effect arising from the lattice and thermal expansion mismatch. Critical current density (J(c)) determined by the magnetization hysteresis loop is as high as 2.2 MA/cm(2) at 4 K under self-field. In-field J(c) characteristics of the film are superior to the bulk crystals. The realization of epitaxial thin films opens opportunities for tuning superconducting properties by epitaxial strain and revealing intrinsic grain boundary transport of Ba1-xKxFe2As2.Y

DOI： 10.1103/physrevmaterials.5.014801

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The influence of chitosan nano-emulsion (CSNe) concentrations on the properties of CSNe reinforced poly (vinyl alcohol) (PVA) nanocomposites is the aim of this study. Polymer solution of CSNe with different concentrations combined with PVA having a low (PVAL) and high (PVAH) molecular weight (Mw), respectively, was fabricated to be the nanocomposite membranes by an electrospinning technique. The morphological characterization of the nanofiber formed in the membranes and the chemical group of PVA and chitosan analysis was performed by scanning electron microscopy (SEM) and Fourier- transform infrared spectroscopy (FTIR), respectively. The tensile properties of all the membrane specimens were tested according to the ASTM D-882. The neat-PVAL and CSNe/PVAL nanocomposite membranes were subjected to the in Vivo test of the open incision on mice. The results showed that an increase of CSNe concentration decreased the viscosity of CSNe-PVA polymer solution but increased the electrical conductivity. Those conditions reduced the nanofiber diameter with various fiber structures. Membranes used PVAL yielded in higher tensile strength and lower tensile modulus than those used PVAH. In Vivo test results of the CSNe/PVAL membrane showed acceptable effectiveness in the wound care treatment to the Sofra-tulle commercial membrane containing antibiotics, and both were better than the neat-PVA membrane. Thus, the CSNe/PVAL provides a promising chance for an alternative wound cover membrane.

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The combination of in-situ and three-dimensional (3D) in transmission electron microscopy (TEM) is one of the emerging topics of recent advanced electron microscopy research. However, to date, there have been only handful examples of in-situ 3D TEM for material deformation dynamics. In this article, firstly, the authors briefly review technical developments in fast tilt-series dataset acquisition, which is a crucial technique for in-situ electron tomography (ET). Secondly, the authors showcase a recent successful example of in-situ specimen-straining and ET system development and its applications to the deformation dynamics of crystalline materials. The system is designed and developed to explore, in real-time and at sub-microscopic levels, the internal behavior of polycrystalline materials subjected to external stresses, and not specifically targeted for atomic resolution (although it may be possible). Technical challenges toward the in-situ ET observation of 3D dislocation dynamics are discussed for commercial structural crystalline materials, including some of the early studies on in-situ ET imaging and 3D modeling of dislocation dynamics. A short summary of standing technical issues and a proposed guideline for further development in the 3D imaging method for dislocation dynamics are then discussed.

DOI： 10.1016/j.cossms.2020.100850

記述言語：英語  

Electron tomography imaging methods with diffraction contrast for materials research
Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) enable the visualization of three-dimensional (3D) microstructures ranging from atomic to micrometer scales using 3D reconstruction techniques based on computed tomography algorithms. This 3D microscopy method is called electron tomography (ET) and has been utilized in the fields of materials science and engineering for more than two decades. Although atomic resolution is one of the current topics in ET research, the development and deployment of intermediate-resolution (non-atomic-resolution) ET imaging methods have garnered considerable attention from researchers. This research trend is probably not irrelevant due to the fact that the spatial resolution and functionality of 3D imaging methods of scanning electron microscopy (SEM) and X-ray microscopy have come to overlap with those of ET. In other words, there may be multiple ways to carry out 3D visualization using different microscopy methods for nanometer-scale objects in materials. From the above standpoint, this review paper aims to (i) describe the current status and issues of intermediate-resolution ET with regard to enhancing the effectiveness of TEM/STEM imaging and (ii) discuss promising applications of state-of-the-art intermediate-resolution ET for materials research with a particular focus on diffraction contrast ET for crystalline microstructures (superlattice domains and dislocations) including a demonstration of in situ dislocation tomography.

DOI： 10.1093/jmicro/dfaa002

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Kyushu University Ultramicroscopy Platform for Nanomaterial Developing

DOI： 10.2320/materia.58.746

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.2320/matertrans.MT-M2019190

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To investigate the precipitation behavior of super duplex stainless steel in its weld by friction stir welding (FSW) at a low welding speed, we carried out microstructural observation and analysis. An intermetallic compound phase, ·, was observed in the heat affected zone (HAZ). The · phase precipitated at the interfaces between ¤-Fe (ferrite) and £ -Fe (austenite) grains 12 mm away from the stir zone (SZ)/HAZ boundary. On the other hand, the Cr₂N was observed together with the belt-like £ -Fe grain aggregates in the vicinity of the advancing side (AS) of the SZ. The other intermetallic phase,», was also observed at a triple junction of £ -Fe grains. This demonstrates that the precipitation of the Cr₂N and» phases correlates with the transformation of ¤-Fe to £A-Fe (secondary austenite).

DOI： 10.2320/matertrans.M2019069

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bi,Pb-2223 phase on SrTiO ₃ (100) fabricated by RF sputtering and annealing method have been investigated. We tried to fabricate Bi,Pb-2223 phase using multilayered precursors of Bi-2212 and Ca-Cu-Pb-O. We fabricated a multilayered film as a precursor by using two kinds of sputtering targets of Bi,Pb-2212 and Ca-Cu-Pb-O. After deposition by sputtering, the multi-layered precursor was annealed with Bi,Pb-2223 pellets at 840 °C for 100 h. From the X-ray diffraction (XRD) measurements, the main peaks of the precursor film were of Bi,Pb-2212 phase, but still remained large impurity phase. From the transmission electron microscopy (TEM) and Scanning Transmission Electron Microscopy (STEM) observation, we confirmed that a multilayer combination of a Bi,Pb-2212 layer and Ca-Cu-Pb-O layer was formed. After annealing, we determined the T _c through resistance measurements. The T _c value determined by the four-probe method was T _c ^zero = 104.K. Furthermore, we observed two phases of Bi,Pb-2223 and Bi,Pb-2212 by XRD measurement. These results suggest that the Bi,Pb-2223 phase transformed from multilayered precursor film of Bi,Pb-2212 and Ca-Cu-Pb-O formed.

DOI： 10.1109/TASC.2019.2907229

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The evolution of intra-and inter-granular structures in Co-doped BaFe₂As₂ (Ba-122) has been studied to address key issues associated with limited inter-granular current transport in randomly oriented polycrystalline Fe-based superconducting materials. We found that the following phenomena occur with an increase in reaction temperature: (i) significant grain growth; (ii) formation and evolution of two types of cracks; (iii) enhancement in the intra-granular current loop; (iv) reduction of magnetic shielding volume; and (v) decrease of the inter-granular transport current. A strong correlation between the inverse grain size and the inter-granular current density was observed. These results indicate that the key microstructural feature to achieve high transport current is a small grain size with no inter-granular cracks, and that low temperature synthesis is an effective path to this end. Based on the observed stacking faults and inter-granular amorphous layers, we propose a model for the formation of the two types of cracks in a polycrystalline Ba-122 phase, i.e. intra-and inter-granular cracks.

DOI： 10.1088/1361-6668/ab0eb6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effects of additional graphite in (Bi
_0.3
Sb
_1.7
Te
_3.1
)
_1−x
C
_x
(x = 0, 0.004, 0.012, 0.032, 0.06, and 0.12) prepared by mechanical alloying followed by hot pressing were investigated. Carbon was added to obtain a low thermal conductivity via phonon scattering. The samples were examined by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy, and electron energy-loss spectroscopy (EELS). EELS can be used to investigate the distributions of light elements such as carbon. The diffraction peaks indicated a single-phase Bi
₂
Te
₃
–Sb
₂
Te
₃
solid solution. All the specimens were p-type semiconductors and SEM and TEM images showed dense without coarse grains. Agglomeration along the grain boundaries and inhomogeneous dispersion of carbon was observed by EELS. (Bi
_0.3
Sb
_1.7
Te
_3.1
)
_0.88
C
_0.12
grains wrapped by carbon layers of thickness approximately 50 nm were observed. The thermal conductivity of (Bi
_0.3
Sb
_1.7
Te
_3.1
)
_1−x
C
_x
increased with increasing x. It is considered that the presence of a large amount of carbon affected the thermal conductivity of the Bi
_0.3
Sb
_1.7
Te
_3.1
matrix because the thermal conductivity of carbon is much higher than that of Bi
_0.3
Sb
_1.7
Te
_3.1
and the carbon was dispersed inhomogeneously. Bi
_0.3
Sb
_1.7
Te
_3.1
without additional graphite had a maximum dimensionless figure of merit ZT = 1.1. The ZT value decreased, and varied from 0.8 to 1.0, for (Bi
_0.3
Sb
_1.7
Te
_3.1
)
_1−x
C
_x
. The results show that inhomogeneously dispersed carbon did not improve the thermoelectric properties of Bi
_0.3
Sb
_1.7
Te
_3.1
.

DOI： 10.1016/j.intermet.2019.03.005

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In-situ straining and electron tomography system: its development and performance

記述言語：日本語  

Placticals and Trends of Electron Tomography for Materials Research

DOI： 10.2320/materia.57.589

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Electron beam spectroscopy has recently attracted much attention in the modal analysis of nanophotonic and plasmonic systems. In principle, electron energy-loss spectroscopy (EELS) provides information about the electromagnetic local density of states of all sorts of electromagnetic modes as well as nonradiative modes. However, there have not been many examples related to the EELS analyses for electromagnetic Bloch modes. Herein, EELS measurements are performed for the characterization of nonradiative band-edge modes facing the first bandgap in a plasmonic crystal with a triangular lattice, which is well-known for its full bandgap formation. The obtained spectrum images clearly determine the characteristics of the lower and upper band-edge modes, compared with an analytical model based on group theory and a numerical simulation by the finite-difference time-domain method. The EELS spectra also reveal differences in the plasmonic density of states between the lower and upper band-edges, which provides information about the band deformation near the bandgap.

DOI： 10.1021/acsphotonics.8b00936

記述言語：その他   掲載種別：研究論文（その他学術会議資料等）  

DOI： 10.1109/INTMAG.2018.8508412

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The synthesis of platinum silicide at a Pt/SiO_x interface by photon irradiation was investigated using transmission electron microscopy. A platinum silicide, Pt₂Si, was successfully formed at the Pt/SiO_x interface by irradiation with 680 and 140 eV photons, but not by irradiation with 80 eV photons. Silicide formation was also induced by irradiation with electrons of energy 75 keV. The amount of silicide formed by photon irradiation was lower than the amount obtained by electron irradiation. Silicide formation by both photon and electron irradiation was accompanied by Si depletion in amorphous SiO_x. The experimental results indicate that silicide formation is induced by electronic excitation. A possible mechanism for silicide formation is proposed on the basis of the results.

DOI： 10.1016/j.actamat.2018.05.045

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Development of an in-situ straining and time-resolved electron tomography data acquisition system

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We elucidate the microstructural evolution in MgB₂ wires fabricated at two different temperatures by the internal Mg diffusion (IMD) method via multiple-scale microstructural observations. The critical current (I_c) of MgB₂ wire was enhanced by the IMD method; however, the I_c of MgB₂ was not sufficiently high to allow its practical applications. To prepare MgB₂ by the IMD method, molten Mg is required to infiltrate the gaps between the B grains and penetrate each B grain. Here, we suggest that controlling the infiltration and penetration behaviors of Mg are key to enhancing the I_c of MgB₂ fabricated by the IMD method. One reason for the decrease in I_c is the existence of residual B grains in the MgB₂ crystalline region, which has an area fraction of 25% even in the MgB₂ wire exhibiting the highest I_c. The amount of residual B grains, which formed due to the insufficient penetration distance of Mg atoms in the B grain, decreased after high-temperature treatment. However, the microstructure of the MgB₂ wire fabricated at a temperature higher than the melting point of Mg was non-uniform because Mg infiltrated the gap between the B grains rapidly and non-uniformly. Thus, optimization of heat treatment temperature can effectively control the infiltration and penetration of Mg in the B grains, yielding uniform microstructures.

DOI： 10.1016/j.jallcom.2018.01.012

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We elucidate the microstructural evolution in MgB2 wires fabricated at two different temperatures by the internal Mg diffusion (IMD) method via multiple-scale microstructural observations. The critical current (I-c) of MgB2 wire was enhanced by the IMD method; however, the I-c of MgB2 was not sufficiently high to allow its practical applications. To prepare MgB2 by the IMD method, molten Mg is required to infiltrate the gaps between the B grains and penetrate each B grain. Here, we suggest that controlling the infiltration and penetration behaviors of Mg are key to enhancing the I-c of MgB2 fabricated by the IMD method. One reason for the decrease in I-c is the existence of residual B grains in the MgB2 crystalline region, which has an area fraction of 25% even in the MgB2 wire exhibiting the highest I-c. The amount of residual B grains, which formed due to the insufficient penetration distance of Mg atoms in the B grain, decreased after high-temperature treatment. However, the microstructure of the MgB2 wire fabricated at a temperature higher than the melting point of Mg was non-uniform because Mg infiltrated the gap between the B grains rapidly and non-uniformly. Thus, optimization of heat treatment temperature can effectively control the infiltration and penetration of Mg in the B grains, yielding uniform micro structures. (C) 2018 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2018.01.012

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effects of thermally stabilized particles on the recrystallization behavior of an AlMgSi alloy were investigated to obtain the fundamental knowledge for controlling the microstructure, texture, and mechanical properties of this alloy. In this study, the AlMgSiScZr alloy was cast, homogenized, and hot-rolled. Three types of spherical Al₃(Sc, Zr) particles with L1₂ structure, rod-like incoherent, spherical semi-coherent, and spherical incoherent particles, were observed in a hot-rolled sample of the AlMgSiScZr alloy using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS). In addition, three-dimensional electron tomography (3D-ET) and STEM-EDS revealed that all particles have a core-shell structure with a Sc-enriched core and a Zr-enriched shell. It is considered that these particles are formed during casting, homogenized treatment, and hot rolling. The crystal orientation distribution of the sample after cold rolling indicated that the presence of Al₃(Sc, Zr) particles may interfere with the recrystallization (grain growth) until 600°C. Comparison with the driving force of primary recrystallization and grain growth, and the pinning force of Al₃(Sc, Zr) particles, showed that these particles mainly contribute to the suppression of grain growth. The results of an in-situ heating SEM/EBSD analysis of the cold-rolled AlMgSiScZr alloy supported this suggestion.

DOI： 10.2320/matertrans.L-M2018802

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Magnetic properties and mechanical properties of high purity Fe-3 mass%Si alloy by cold crucible levitation melting was investigated. The raw material of the alloy made from electrolytic iron and pure silicon with a purity of 99.99 mass% and 99.999 mass% in amount of impurities excluding Fe and Si were suppressed to 90 ppm or less. In the magnetic property, the iron loss of the alloy was reduced to a third of 35H210, a silicon steel sheet of the same Si composition commercially. This reduction shows the effect of high purity. In the magnetic domain observation, the equal behavior as magnetic properties was observed. In mechanical property, it proved that the high purity Fe-3 mass% Si alloy was easy to draw because the elongation of the alloy was higher than the commercially available silicon steel sheet.

DOI： 10.2320/jinstmet.J2018008

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The yield strength and work hardening of Al.Mg.Si alloys are related to the concentration of solute atoms. This study was carried out to clarify the effect of two kinds of solute atoms on these properties in terms of a linear combination of contributions from a solid solution. Tensile tests were conducted with Al and with Al.0.62Mg-0.32Si, Al.0.65Mg.0.81Si, Al.2.4Mg and Al.4.4Mg (mass%) alloys in solid solution. Work hardening was analysed using the Kocks .Mecking model, yielding two parameters which indicate the storage and recovery of dislocations in the material. The yield strength could not be expressed as a linear combination of solute atom concentrations, but the amount of dislocation storage and dynamic recovery could be expressed as such linear combinations. In the high.strain region, the Kocks .Mecking model no longer applies, and the maximum stress at which the model failed increased with increasing concentrations of solute atoms. It is generally known that an interaction between strain fields around solute atoms and quenched.in vacancies can affect the yield strength owing to dislocation motion and that these atoms can retard the development of microstructure in high.strain regions. A linear combination of contributions from solid solutions is possible only for the storage and recovery of dislocations in the low.strain region.

DOI： 10.2320/jinstmet.J2018015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

For the purpose of higher welding speed and lower force in friction-stir-welding (FSW), we investigated the feasibility of preheating using gas-tungsten- arc-welding (GTAW). It can be expected to assist heat input for the plastic flow by using GTAW with high energy density. Defect-free bonding by a GTAW-FSW hybrid process was successfully achieved at a welding speed less than 8.3mm/s, while normal FSW left a defect at welding speed of 5.0mm/s. The axial forces during friction stirring in the GTAW-FSW process were lower than 40% of that in the normal FSW. The joints of GTAW-FSW had stir zones with fine grains similar to the FSW joints. This process could obtain higher productivity, that is, higher welding speed and lower force than the conventional FSW. It is also possible to obtain a high strengthen and unique structure with fine grains of FSW.

DOI： 10.2207/qjjws.36.26

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In conventional transmission electron microscopy, specimens to be observed are placed in between the objective lens pole piece and therefore exposed to a strong magnetic field about 2 T. For a ferromagnetic specimen, magnetization of the specimen causes isotropic and anisotropic defocusing, deflection of the electron beam as well as deformation of the specimen, which all become more severe when the specimen tilted. Therefore electron tomography on a ferromagnetic crystalline specimen is highly challenging because tilt-series data sets must be acquired without changing the excitation condition of a specific diffraction spot. In this study, a scanning transmission electron microscopy (STEM) tomography method without magnetizing a ferromagnetic specimen has been developed for three-dimensional (3D) visualization of dislocations in α-Fe, which is a typical ferromagnetic material. Magnetic-field-free environment down to 0.38 ± 0.07 mT at the specimen position is realized by demagnetizing the objective lens pole piece of a commercial STEM instrument. By using a spherical aberration corrector with the magnetic-field-free environment, an “aberration corrected Low-Mag STEM mode” with no objective lens field reaches a convergence semi angle ∼1 mrad and a spatial resolution ∼5 nm, and shows an adequate performance of imaging dislocations under a two-beam excitation condition for a low-index diffracted beam. The illumination condition for the aberration corrected Low-Mag STEM mode gives no overlap between the direct beam disk (spot) and neighboring diffraction disks. An electron channeling contrast imaging technique, in which an annular detector was located at a doughnut area between the direct beam and the neighboring diffracted beams, was effectively employed with the aberration corrected Low-Mag STEM mode to keep image intensity high enough even at large specimen-tilt angles. The resultant tomographic observation visualized 3D dislocation arrangements and active slip planes in a deformed α-Fe specimen.

DOI： 10.1016/j.ultramic.2017.07.016

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Hydrogen embrittlement is a serious problem in high-strength steels. Drawn pearlitic steel shows excellent resistance to hydrogen embrittlement despite its high strength, and aging treatment at a low temperature can simultaneously improve its strength and hydrogen-embrittlement resistance. To clarify the mechanism for this we have used thermal desorption analysis (TDA) and the newly developed precession electron diffraction analysis method in the transmission electron microscope. After aging at 100 °C for 10 min, the amount of hydrogen seen amount on the TDA curve reduced at around 100 °C. In contrast, when aging was performed at 300 °C, the hydrogen amount further reduced at around 100 °C and the unevenly deformed lamellar ferrite zone was locally recovered. For the samples that were aged at the low temperature, we confirmed that their yield strength and relaxation stress ratios increased simultaneously with improvement in the hydrogen-embrittlement property. We infer that segregation of carbon or formation of very fine carbide in dislocations during aging is the cause of these behaviors.

DOI： 10.1088/1757-899X/219/1/012026

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sn-Ag-Cu alloy used in the present study is commercial Sn-3.0Ag-0.5Cu solder ball alloys with a diameter of 400 and 300 μm which were long term atmospheric oxidized for about 6 years (specimen-1) and under high temperature/humidity at 85°C and relative humidity of 85% for 2140 h, respectively. Morphologies and nanostructure of the oxide nanolayers formed on the surface of Sn-Ag-Cu alloys were studied from the interface of the oxide film and the tin substrate by transmission electron microscopy (TEM) to verify the oxidation mechanism. Cross-sectional TEM specimens were prepared using a focused-ion-beam (FIB) micro-sampling technique. Before the FIB fabrication, the specimen surface was coated with carbon (C) and tungsten (W) films. Inhomogeneous thickness of tin-oxide nanolayer formed on specimen-1 and specimen-2 were fluctuated between 20-40 nm and 40-50 nm, respectively. The nanolayer on specimen-1, however, consists of polycrystalline SnO and SnO₂, whereas the one on the specimen-2 comprises of polycrystalline SnO₂. High resolution (HRTEM) image and fast Fourier transformation (FFT) spectra corresponding to the interface and the substrate areas have confirmed those results. The results verify that at very long atmospheric oxidation Sn was gradually oxidized to be SnO (Sn²⁺) and then SnO₂ (Sn⁴⁺), in which SnO is present at the region closed to interface between Sn-substrate and the tin-oxide layer. At high temperature oxidation, however, Sn was completely oxidized to be SnO₂.

DOI： 10.1088/1757-899X/196/1/012006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This paper reports the preliminary results of a new in-situ three-dimensional (3D) imaging system for observing plastic deformation behavior in a transmission electron microscope (TEM) as a directly relevant development of the recently reported straining-and-tomography holder [ Sato K et al. (2015) Development of a novel straining holder for transmission electron microscopy compatible with single tilt-axis electron tomography. Microsc. 64:369-375]. We designed an integrated system using the holder and newly developed straining and image-acquisition software and then developed an experimental procedure for in-situ straining and time-resolved electron tomography (ET) data acquisition. The software for image acquisition and 3D visualization was developed based on the commercially available ET software TEMography (TM). We achieved time-resolved 3D visualization of nanometer-scale plastic deformation behavior in a Pb-Sn alloy sample, thus demonstrating the capability of this system for potential applications in materials science.

DOI： 10.1093/jmicro/dfw109

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The tensile properties of an Al-Mg-Si alloy with Mg-Si clusters were compared with those of an Al-Mg-Si alloy with β^′′ precipitates of the same strength. The elongation of the alloy with Mg-Si clusters was found to be greater than that of the alloy with β^′′ precipitates because of the high work hardening rate of the former alloy, particularly in the high-strain region. Decomposition of Mg-Si clusters into solute Mg and Si atoms during the tensile deformation was revealed by differential scanning calorimetry. Transmission electron microscopy revealed three types of dislocation characteristics in these alloys: homogeneous distribution of dislocations with β^′′ precipitates, cell structures in the alloy with solute Mg and Si, and a combination of these two types in the alloy with Mg-Si clusters. In the case of the alloy with Mg-Si clusters, the yield strength increased significantly owing to the dislocation cutting mechanism; simultaneously, the elongation of this alloy improved greatly because of the presence of solute Mg and Si atoms formed by decomposition via plastic deformation, which were inferred to prevent dynamic recovery in the later stage of tensile deformation. Consequently, a comparison of conventional 6000 series and 7000 series Al alloys revealed that the alloy with clusters had advantages over the alloy with precipitates and the alloy with solutes in terms of the balance between strength and elongation.

DOI： 10.2320/matertrans.M2016258

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This paper reports the preliminary results of a new in-situ three-dimensional (3D) imaging system for observing plastic deformation behavior in a transmission electron microscope (TEM) as a directly relevant development of the recently reported straining-and-tomography holder [Sato K et al (2015) Development of a novel straining holder for transmission electron microscopy compatible with single tilt-axis electron tomography. Microsc. 64: 369-375]. We designed an integrated system using the holder and newly developed straining and image-acquisition software and then developed an experimental procedure for in-situ straining and time-resolved electron tomography (ET) data acquisition. The software for image acquisition and 3D visualization was developed based on the commercially available ET software TEMography(TM) We achieved time-resolved 3D visualization of nanometer-scale plastic deformation behavior in a Pb-Sn alloy sample, thus demonstrating the capability of this system for potential applications in materials science.

DOI： 10.1093/jmicro/dfw109

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Through using in-situ electron back-scattered diffraction and uniaxial tensile tests, this work mainly focuses on the deformation behavior of retained austenite (RA) in a low-carbon quenching and partitioning (Q&P) steel. In this paper, three different types of RA can be distinguished from different locations, respectively, RA grains at the triple edges, twinned austenite and RA grains positioned between martensite. The results have shown that grains at the triple edges and twinned austenite could transform easily with increasing strain, i.e. are less stable when compared with RA grains distributed between martensite that could resist a larger plastic deformation. Meanwhile, the strain leads to rotations of RA grains distributed at the triple edges and between martensite. Moreover, RA grains with a similar orientation undergone similar rotations with the same true strain. These RA grains rotated along a specific slip plane and slip direction and the grain rotation is taken as a significant factor to improve the ductility of steel. In addition, grain sizes of RA decreased gradually with an increase of true strain and smaller (0–0.2 μm) grains were more capable of resisting the deformation. According to kernel average misorientation (KAM) analysis, it can be found that strain distribution is preferentially localized near martensite–austenite phase boundaries and in the interior of martensite. The average KAM values increased continuously with increasing true strain.

DOI： 10.1016/j.matchar.2016.06.020

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Development of a novel straining holder for TEM compatible with electron tomography

DOI： 10.1002/9783527808465.EMC2016.6262

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Perovskite-type oxides have been widely applied in heterogeneous catalytic reactions, such as soot oxidation. However, a poor contact point between the catalyst and solid reactant (soot) often limits the catalytic performance. Here, we report La_{1 - x}Sr_xCo_0.2Fe_0.8O_{3 - δ} perovskite oxide catalysts with a unique three-dimensional (3D) fiber web structure that increases the high-contact area by trapping soot in the unique pore structure for effective catalytic activity. This feature was carefully analyzed using scanning transmission electron microscopy (STEM) tomography to investigate the location of the soot on the web. The structure of the web, with a thickness of approximately 55 μm, indicated that the soot particles were caught by the 3D pores between the fibers. The relationship between the Sr amount and activate oxygen was also characterized by means of XPS. The results show that the Sr amount of 0.4 produced the highest amount of active oxygen species (O^-) that are essential for soot oxidation reaction. The developed catalyst exhibited a good catalytic performance due to the optimized perovskite chemical structure and the greatly increased number of the contact points owing to the 3D inter-fiber spaces. Hence, our proposed approach is reasonable for application to real soot combustion processes and can also be easily extended to numerous other catalytic processes to enhance the catalytic activity.

DOI： 10.1016/j.apcatb.2016.03.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.

DOI： 10.1007/s12613-016-1306-0

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Deformation and dissolution behaviors are important characteristics of soft dispersion particles in steel to improve the deformability of high strength steel sheets by controlling the work hardening/softening and fracture processes associated with particle dispersion strengthening. In this study, the deformation and dissolution behaviors of ϵ-Cu precipitate particles in a ferrite matrix were investigated to understand how relatively soft dispersion particles influence mechanical responses of the steel compared to hard dispersion particles such as alloy carbides. 35 nm diameter nearly spherical ϵ-Cu particles were initially elongated along the rolling direction by cold rolling, and then these were partly dissolved into the ferrite matrix as the equivalent strain increased. The dissolution of the Cu particles was suggested to be caused by a dynamic partitioning of Cu atoms from the precipitates into the matrix by dislocation shearing at the particle tip sharpened by severe cold working. Simultaneously, the contribution of the ϵ-Cu particles to the dispersion strengthening appeared to be decreased with increasing dislocation density in the matrix during cold rolling. The dislocation density and other defects in the ϵ-Cu particles also increased and the particle/matrix interfaces were serrated or became indistinct as deformation progressed. The morphology, internal defects, and interface structure changes of fine dispersion particles and their correlation with mechanical responses of the alloy are discussed in reference to an identically processed, hard particles dispersed Fe-V binary alloy.

DOI： 10.1016/j.actamat.2016.03.018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Deformation and dissolution behaviors are important characteristics of soft dispersion particles in steel to improve the deformability of high strength steel sheets by controlling the work hardening/softening and fracture processes associated with particle dispersion strengthening. In this study, the deformation and dissolution behaviors of epsilon-Cu precipitate particles in a ferrite matrix were investigated to understand how relatively soft dispersion particles influence mechanical responses of the steel compared to hard dispersion particles such as alloy carbides. 35 nm diameter nearly spherical e-Cu particles were initially elongated along the rolling direction by cold rolling, and then these were partly dissolved into the ferrite matrix as the equivalent strain increased. The dissolution of the Cu particles was suggested to be caused by a dynamic partitioning of Cu atoms from the precipitates into the matrix by dislocation shearing at the particle tip sharpened by severe cold working. Simultaneously, the contribution of the epsilon-Cu particles to the dispersion strengthening appeared to be decreased with increasing dislocation density in the matrix during cold rolling. The dislocation density and other defects in the epsilon-Cu particles also increased and the particle/matrix interfaces were serrated or became indistinct as deformation progressed. The morphology, internal defects, and interface structure changes of fine dispersion particles and their correlation with mechanical responses of the alloy are discussed in reference to an identically processed, hard particles dispersed Fe-V binary alloy. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2016.03.018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Creep and anelastic backflow behaviors of pure copper (4N Cu) with grain size d_g=40 μm were investigated at low temperatures of T<0.3T_m (T_m is melting point) and ultra-low creep rates of ɛ˙=1×10⁻¹⁰s⁻¹ by a high strain-resolution measurement (the helicoid spring specimen technique). Analysis of creep data was based on the scaling factors of creep curves instead of the conventional extrapolated steady-state creep rate. Power-law creep equation is suggested to be the best for describing the primary transient creep behavior, because the pre-parameter does not apparently change with elapsed time. The observed anelastic strains are 1/6 of the calculated elastic strains, and linear viscous behavior was identified from the logarithm plot of the anelastic strain rate versus anelastic strain (slope equals 1). Therefore, the creep anelasticity is suggested to be due to the unbowing of there-dimensional network of dislocations.

DOI： 10.1016/S1003-6326(16)64285-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The microstructure of an AlN template after high-temperature annealing was investigated by transmission electron microscopy (TEM). The AlN template was prepared by depositing an AlN layer of about 200nm thickness on a sapphire (0001) substrate by metal-organic vapor phase epitaxy. The AlN template was annealed under (N₂ + CO) atmosphere at 1500-1650 °C. TEM characterization was conducted to investigate the microstructural evolution, revealing that the postannealed AlN has a two-layer structure, the upper and lower layers of which exhibit Al and N polarities, respectively. It has been confirmed that postannealing is an effective treatment for controlling the microstructure.

DOI： 10.7567/APEX.9.065502

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An aluminium nitride (AlN) buffer layer with 200 nm thickness was grown on (0001) sapphire substrate using the metal-organic vapour phase epitaxy (MOVPE) method in a low-pressure furnace, followed by a clean-up treatment of sapphire substrate at 1100°C. Thereafter, the AlN buffer layer was annealed at a high temperature in the range of 1500°C to 1700°C for 2 hours under the atmosphere of N₂+CO. The objective of this research is to determine the microstructure changes with different annealing temperatures. Cross-sectional TEM has revealed that, after annealing at 1500°C, two types of defects remained in the AlN buffer layer: inverted cone shape domains and threading dislocations. The former domains were observed in an image taken with diffraction of g=0002, but not in an image with g=1010. The morphology and the diffraction condition for the image contrast strongly, suggesting that the domains are inversion domains. The threading dislocations were invisible in the image taken with the diffraction of g=0002, revealing that they were a-Type dislocations. However, after annealing at 1600oC, the inversion domains coalesced with each other to give a two-layer structure divided by a single inversion domain boundary at the centre of the AlN buffer layer. The density of threading dislocation was roughly estimated to be 5×109 cm^-2 after annealing at 1500°C, and to be reduced to 5×10⁸ cm^-2 after annealing at 1600°C. These experimental results validate the fact that the annealing temperature around 1600°C is high enough to remove the defects by the diffusion process. Therefore, it was discovered that high temperature annealing is an effective treatment to alter the microstructure of AlN thin films and remove defects by the diffusion process. Annealing at high temperature is recommended to increase the emission efficiency for fabrication of optoelectronic devices.

DOI： 10.15282/jmes.10.1.2016.14.0182

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present a study concerning Fe–0.176C–1.31Si–1.58Mn–0.26Al–0.3Cr (wt%) steel subjected to a quenching and partitioning (Q&P) process. The results of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and tensile tests demonstrate that the microstructures primarily consist of lath martensite, retained austenite, lower bainite (LB), and a small amount of tempered martensite; moreover, few twin austenite grains were observed. In the microstructure, three types of retained austenite with different sizes and morphologies were observed: blocky retained austenite (~300 nm in width), film-like retained austenite (80–120 nm in width), and ultra- fine film-like retained austenite (30–40 nm in width). Because of the effect of the retained austenite/martensite/LB triplex microstructure, the specimens prepared using different quenching temperatures exhibit high ultimate tensile strength and yield strength. Furthermore, the strength effect of LB can partially counteract the decreasing strength effect of martensite. The formation of LB substantially reduces the amount of retained austenite. Analyses of the retained austenite and the amount of blocky retained austenite indicated that the carbon content is critical to the total elongation of Q&P steel.

DOI： 10.1007/s12613-016-1239-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54ks down to 67.4 HV at 360ks, below the initial hardness value, 71.8 HV at 0ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al₃Sc_1-xZr_x and also block-shaped Al₃Sc precipitates growing along <100>_Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al₃Sc.

DOI： 10.1016/j.micron.2015.12.002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report an in-situ study of the deformation-induced rotation and transformation of austenite grains in a low-carbon steel treated by the quenching and partitioning process using electron back-scattered diffraction and uniaxial tension experiments. It was found that retained austenite could be classified into four types according to different locations in the microstructure: retained austenite at triple edges, twinned austenite, retained austenite distributed between martensite and retained austenite embedded completely in a single ferrite. The results showed that at the early stage of deformation, the retained austenite at the triple edges and twinned austenite transformed easily, while the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite rotated with no transformation; and did not transform until a large deformation was provided. This phenomenon implies that the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite are more capable of resisting deformation. From the observations of Schmid factor maps and the texture of retained austenite, it can be concluded that the rotation of retained austenite followed a particular slip plane and slip direction. Moreover, the rotation of retained austenite could improve the ductility of the material. In comparison with the film-like retained austenite distributed between martensite, the retained austenite embedded completely in a single ferrite could resist a larger rotation angle, i.e. the latter could contribute more to the ductility of the steel. In addition, from the analysis of kernel average misorientation that the strain distribution mainly concentrated near the α - γ phase boundaries and in the interior of martensite, and the rotation angles and dislocation density of austenite increase with increasing strain.

DOI： 10.1016/j.msea.2015.09.076

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report an in-situ study of the deformation-induced rotation and transformation of austenite grains in a low-carbon steel treated by the quenching and partitioning process using electron back-scattered diffraction and uniaxial tension experiments. It was found that retained austenite could be classified into four types according to different locations in the microstructure: retained austenite at triple edges, twinned austenite, retained austenite distributed between martensite and retained austenite embedded completely in a single ferrite. The results showed that at the early stage of deformation, the retained austenite at the triple edges and twinned austenite transformed easily, while the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite rotated with no transformation
and did not transform until a large deformation was provided. This phenomenon implies that the retained austenite at the boundaries between martensite and that embedded completely in a single ferrite are more capable of resisting deformation. From the observations of Schmid factor maps and the texture of retained austenite, it can be concluded that the rotation of retained austenite followed a particular slip plane and slip direction. Moreover, the rotation of retained austenite could improve the ductility of the material. In comparison with the film-like retained austenite distributed between martensite, the retained austenite embedded completely in a single ferrite could resist a larger rotation angle, i.e. the latter could contribute more to the ductility of the steel. In addition, from the analysis of kernel average misorientation that the strain distribution mainly concentrated near the α - γ phase boundaries and in the interior of martensite, and the rotation angles and dislocation density of austenite increase with increasing strain.

DOI： 10.1016/j.msea.2015.09.076

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have performed combined high-resolution microstructural and grain orientation analyses to understand the key microstructural factors associated with high intergranular transport current in polycrystalline bulk forms of MgB2. The ex-situ method can produce MgB2 with relatively high packing factors; nevertheless, the connectivity of MgB2 fabricated by the ex-situ method (ex-situ MgB2) was less than that of in-situ MgB2. The poor connections between MgB2 grain aggregates cause the low connectivity of ex-situ MgB2. Plate-like pores are present between the aggregates of MgB2 grains in ex-situ MgB2; these pores remain even after prolonged self-sintering at high temperatures. In addition, MgB2 crystals decompose to MgB4 in sintering for a long period. Moreover, MgO particles are formed between MgB2 grain aggregates and inhibit interaggregate connections. In contrast, in-situ MgB2 fabricated at the same sintering conditions exhibits spherical pores between MgB2 grains, resulting in a uniform pore distribution and intergranular connection. These problems must be addressed to further enhance the connectivity in ex-situ MgB2. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.09.253

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have performed combined high-resolution microstructural and grain orientation analyses to understand the key microstructural factors associated with high intergranular transport current in polycrystalline bulk forms of MgB₂. The ex-situ method can produce MgB₂ with relatively high packing factors; nevertheless, the connectivity of MgB₂ fabricated by the ex-situ method (ex-situ MgB₂) was less than that of in-situ MgB₂. The poor connections between MgB₂ grain aggregates cause the low connectivity of ex-situ MgB₂. Plate-like pores are present between the aggregates of MgB₂ grains in ex-situ MgB₂; these pores remain even after prolonged self-sintering at high temperatures. In addition, MgB₂ crystals decompose to MgB₄ in sintering for a long period. Moreover, MgO particles are formed between MgB₂ grain aggregates and inhibit interaggregate connections. In contrast, in-situ MgB₂ fabricated at the same sintering conditions exhibits spherical pores between MgB₂ grains, resulting in a uniform pore distribution and intergranular connection. These problems must be addressed to further enhance the connectivity in ex-situ MgB₂.

DOI： 10.1016/j.jallcom.2015.09.253

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with-5.0 mm (=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging.

DOI： 10.2355/isijinternational.ISIJINT-2015-735

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To evaluate heterogeneous strain distribution developed by pre-deformations in dual phase (DP) steel accurately, a combinational technique of Electron Backscatter Diffraction (EBSD) and Digital Image Correlation (DIC) methods was newly introduced in this study. A good correlation is established between kernel average misorientation calculated by EBSD and local equivalent strain measured by DIC in ferrite matrix of DP steels regardless of the difference in deformation process, which means that an EBSD orientation map can be easily converted into an applicative strain map by employing the individual correlation formula. This new technique reveals that very large strain region is locally formed within dozens of micrometer from the punched edge in a punched DP steel. On the other hand, hard martensite grains dispersed in DP steel remarkably promote the heterogeneity of strain distribution in ferrite matrix. As a result, the large strain region is also developed in the form of bands in a cold-rolled DP steel by only 60% thickness reduction at least, as if it is affected by the distribution and morphology of martensite grains. In addition, the local strain mapping demonstrates that the equivalent strain of the large strain band in cold-rolled material is comparable to that of the heavily deformed edge in punched one. The very large strain band in ferrite matrix is characterized by ultrafine grained structure, which leads to the possibility for the losing ductility in ferrite matrix and the martensite cracking.

DOI： 10.2355/isijinternational.ISIJINT-2016-310

記述言語：英語   掲載種別：研究論文（学術雑誌）  

To evaluate heterogeneous strain distribution developed by pre-deformations in dual phase (DP) steel accurately, a combinational technique of Electron Backscatter Diffraction (EBSD) and Digital Image Correlation (DIC) methods was newly introduced in this study. A good correlation is established between kernel average misorientation calculated by EBSD and local equivalent strain measured by DIC in ferrite matrix of DP steels regardless of the difference in deformation process, which means that an EBSD orientation map can be easily converted into an applicative strain map by employing the individual correlation formula. This new technique reveals that very high strain region is locally formed within dozens of micrometer from the punched edge in a punched DP steel. On the other hand, hard martensite grains dispersed in DP steel remarkably promote the heterogeneity of strain distribution in ferrite matrix. As a result, the high strain region is also developed in the form of bands in a cold-rolled DP steel by only 60% thickness reduction at least, as if it is affected by the distribution and morphology of martensite grains. In addition, the local strain mapping demonstrates that the equivalent strain of the high strain band in cold-rolled material is comparable to that of the heavily deformed edge in punched one. The very high strain band in ferrite matrix is characterized by ultrafine grained structure, which leads to the possibility for the losing ductility in ferrite matrix and the martensite cracking.

DOI： 10.2355/tetsutohagane.TETSU-2015-086

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Highly luminescent red emitting Gd₂O₃:Eu³⁺, Li⁺ nanophosphor has been synthesized by the solvothermal combustion of the metal-citrate complex in diethylene glycol medium. The morphology and luminescence properties of these nanophosphors are found to be highly sensitive to the extent of lithium ion compensation. It is found that lithium ions promote grain growth and alter the morphology of the Gd₂O₃:Eu³⁺ nanophosphor from nearly spherical to cobblestone like. A significant enhancement in intensity of luminescence and quantum efficiency is observed in lithium compensated nanophosphors. The highest emission intensity is observed for the Gd_1.75Eu_0.1Li_0.15O₃ nanophosphor, about 1.83 times that of Gd_1.9Eu_0.1O₃ and is attributed to the enhanced intra 4f-4f emission transitions arising from the modifications of the crystal field and distortion of the local symmetry around the europium ions. The luminescence decay profiles are found to be single exponential in nature and the lifetime measured was 1.36 ms for the Gd_1.75Eu_0.1Li_0.15O₃ nanophosphor. The chromaticity coordinates of these nanophosphors indicated high colour purity. Judd-Ofelt intensity parameters indicated that lithium compensation increases the polarization of the local environment and an increase of covalency and asymmetry around the europium ions.

DOI： 10.1039/c5ra26095g

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The author has contributed to developing sample holders for electron tomography (ET) [1, 2]. Based on the author’s experience of the holder development, there are distinctive issues of designing ET holders. Because ET usually needs high-angle sample tilt over 60 degrees, the information of a pole piece gap in a transmission electron microscope (TEM) is necessary and also unsatisfactory for designing sample holders capable of ET observation. Firstly, the eucentric height of a sample holder may not locate at the center of the pole piece gap. Secondly, there may not be an enough space (vertical and horizontal widths) outside the pole piece gap. These issues in the TEM sample chamber make the compatibility of high-angle tilt and desirable functions in an ET sample holder difficult. It is also an issue for ET that insertion of an objective aperture limits the maximal sample-tilt angle in modern TEMs of which the objective lens systems are optimized for high-resolution scanning transmission electron microscopy (STEM) as well as transmission electron microscopy (TEM). Therefore, using an objective aperture for diffraction contrast ET observation [3, 4] is not available in these modern TEMs. Alternative diffraction contrast ET observation methods without using an objective aperture have been reported [5, 6]. Fast tilt-series datasets acquisition for time-resolved ET [7] needs superior performances of a TEM goniometer system as well as an image acquisition system. Based on the author‘s experience of fast tilt-series datasets acquisition [8], the followings are issues of the goniometer system for high-resolution time-resolved ET imaging: controllable sample tilt speed at a user level; accurate readout of sample tilt angles synchronizing with image acquisition; (iii) a stable eucentric position of a field of view during sample tilt.

DOI： 10.1093/jmicro/dfw083

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effects of thermally stabilized particles in Al-Mg-Si alloy on recrystallization behavior were investigated to obtain fundamental knowledge to control microstructure, texture and mechanical properties of this alloy. In this study, the Al-Mg-Si-Sc-Zr alloy was cast, homogenized and hot rolled. Three types of spherical Al3(Sc, Zr) particles with L12 structure: Rod-like incoherent, spherical semi-coherent and spherical incoherent particles were observed in the hot-rolled sample in the Al-Mg-Si-Sc-Zr alloy by using TEM, STEM and EDS. In addition, it was found that all particles have the core-shell structure with the core enriched with Sc and the shell enriched with Zr atoms by 3D-ET and STEM-EDS. It is considered that these particles are formed during casting, homogenized treatment and hot rolling. The results of crystal orientation distribution of annealed sample after cold rolling indicated that the presence of Al3(Sc, Zr) particles may interfere with the recrystallization (the grain growth) until 600°C. From the comparison with the driving force of primary recrystallization and grain growth, and the pinning force of Al3(Sc, Zr) particles, it was suggested that these particles mainly contribute to the suppression of grain growth. The results of in-situ heating SEM/EBSD analysis of cold rolled Al-Mg-Si-Sc-Zr alloy supported the suggestion.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

MgB₂ is one of the "low activation superconductors", because the half-life of the induced radio-activity on the MgB₂ is much shorter than that of Nb-based superconductors such as NbTi, Nb₃Sn and Nb₃Al. MgB₂ wire would become an alternative material for Nb-Ti wire for the Poloidal Field and correction feedback coils, if the critical current density (J_c) around the magnetic field of 4 T could be improved. We found that addition of Cu using the compound Mg₂Cu was an effective method to enhance J_c and succeed to fabricate 100 m length of MgB₂ wire with Cu addition. J_c of the 100 m long MgB₂ with Cu addition was comparable to that of a NbTi wire, and the small solenoid coil using Cu added MgB₂ wire reached a central magnetic field of 2.62 T. We found that MgB₂ wire is an alternative material to commercial NbTi wires under the hard neutron irradiation in a fusion reactor. Furthermore, we also fabricated a Cu added MgB₂ wire using isotope pure boron-11 (¹¹B) powder as the boron source to reduce the radioactivity. The critical temperature (T_c) of the MgB₂ wire using ¹¹B powder was found to be 37 K, and T_c was found to be changed by different boron materials.

DOI： 10.1016/j.fusengdes.2015.05.005

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A transmission electron microscope (TEM) based orientation mapping technique and micromagnetic simulations were applied to study the influence of easy axis distribution (EAD) on magnetic properties of FePt-C granular films which were deposited on a single crystalline MgO (0 0 1) substrate and a (0 0 1)-textured poly-crystalline MgO underlayer. The FePt-C film on the polycrystalline MgO underlayer shows smaller perpendicular coercivity, broader switching field distribution and visible in-plane minor loop compared with that deposited on the single crystalline MgO (0 0 1) substrate. Although the grain sizes and their distributions in both films look similar in TEM, orientation mapping and texture analysis revealed that the polycrystalline MgO underlayer introduces significant misorientation in the (0 0 1)-textured FePt grains. Micromagnetic simulations successfully reproduced the large hysteresis in the in-plane magnetization by introducing the specific misorientation distribution of the FePt grains obtained from the texture analysis. The misoriented FePt grains were found to be grown from misoriented MgO grains, indicating that the improvement of the (0 0 1) texture of the MgO underlayer is essential to reduce the in-plane component of FePt based recording media.

DOI： 10.1016/j.actamat.2015.03.007

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The uniform single phase Bi,Pb-2223 films are needed in order to acquire fundamental superconductivity data for the development of Bi,Pb-2223 wires. However, Bi,Pb-2223 films that we previously reported had the non-uniform microstructure containing several other phases. In this study we investigated the microstructural evolution during the heat treatment and processing route to fabricate uniform Bi,Pb-2223 films elucidated. An as-grown film had a small amount of Bi-2223 phase and a large amount of Ca-Sr-Cu-O phase. C-axes of some Bi-2223 crystals are not aligned along the normal direction of the STO substrate. In the primary stage of heat treatment, the formation of Bi,Pb-2223 phase proceeds. In the second stage of heat treatment, although the flat Cu-O layers in the Bi,Pb-2223 phase are formed by liquid-phase reactions, the grain coarsening of Ca-Sr-Cu-O phase also occurs. From the observation results, the fabrication process should be optimized based on the following points: uniform dispersion of penetration (diffusion) paths of Pb atoms into the film; short duration of heat treatment to avoid phase separation of Bi,Pb-2223 and coarsening of Ca-Sr-Cu-O phase.

DOI： 10.1109/TASC.2014.2382874

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The ex situ method yields MgB₂ samples with high packing factor. However, the critical current density of MgB₂ bulks and wires fabricated using the ex situ method (ex situ MgB₂) requires improvement for practical use because of insufficient connectivity. In this study, we evaluated the microstructure of self-sintered ex situ MgB₂ bulks fabricated from laboratory-made ball-milled powder. We observed that green compacts of the ball-milled bulks contain fine MgB₂ grain aggregates and a decreased gap length between MgB₂ grain aggregates compared with those prepared without ball-milling. Therefore, the number of connections between the MgB₂ grain aggregates and current path increased. However, the width of the connections between MgB₂ grain aggregates remained narrow, suggesting the importance of controlling the initial microstructure of green compacts, such as the size of MgB₂ grain aggregates and packing factor, by optimizing milling and pressing conditions.

DOI： 10.1109/TASC.2014.2379928

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thin films of Bi-2223 fabricated on SrTiO₃(100) substrates by dc sputtering were found to have a transition temperature (Tc) as low as that of bulk-phase Bi-2223. Subsequent annealing of these precursor films in the presence of Bi,Pb-2223 pellets increased this Tc value from 72 to 105 K, making it comparable to bulk-phase Bi,Pb-2223. Strong (00l) peaks and a sharp quadrupole were observed in this annealed film, indicating a main phase of Bi,Pb-2223 with a c-axis orientation by the X-ray diffractometry (XRD) measurements. A maximum critical current density (Jc) of 3.3 × 105 A/cm² at 77 K was also obtained with the Bi,Pb-2223 thin film, which is a value that is much higher than that of commercial Bi,Pb-2223 tapes. Jc values of thin films were strongly dependent on the annealing temperatures between 854 ^°C and 866 ^°C. In this temperature range, XRD data show that the thin films were not a single phase of Bi,Pb-2223, suggesting only a slight interruption of the supercurrent. Although, the films have a good c-axis and ab-axis alignments. Thus, although the films were not perfect, the improvement in microstructure allows for a much higher Jc value.

DOI： 10.1109/TASC.2014.2376193

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We performed the three-dimensional visualization of dislocations through serial sectioning and use of SEM electron channeling contrast (ECC) images for a crept nickel-based alloy. We successfully reconstructed a volume of approximately 7.5 μm³, including dislocation arrangements, by performing calculations based on the continuous tomograms of ECC images. By incorporating the information on crystal orientation obtained by the electron back-scattered diffraction, we verified that the three-dimensional arrangement of dislocations, such as slip plane, was accurately reflected in the three-dimensional volume.

DOI： 10.1016/j.scriptamat.2015.02.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We performed the three-dimensional visualization of dislocations through serial sectioning and use of SEM electron channeling contrast (ECC) images for a crept nickel-based alloy. We successfully reconstructed a volume of approximately 7.5 mu m(3), including dislocation arrangements, by performing calculations based on the continuous tomograms of ECC images. By incorporating the information on crystal orientation obtained by the electron back-scattered diffraction, we verified that the three-dimensional arrangement of dislocations, such as slip plane, was accurately reflected in the three-dimensional volume. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd.

DOI： 10.1016/j.scriptamat.2015.02.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Noble Au@PdAg and Au@PdAg@Ag core-shell nanorods (NRs) having PdAg alloy shells were synthesized using Au@Pd NRs as seeds. Their crystal structures and growth mechanisms were examined using data from TEM, TEM-EDS, XRD, and UV-Vis-NIR extinction spectroscopy. First, cuboid or dumbbell-type Au@Pd NR seeds were prepared using Au NRs as seeds. In the second step, when Ag⁺ ions were reduced over these seeds, cuboid and dumbbell-type Au core PdAg alloy shell NRs were formed with maximum Ag content of about 16% and 24%, respectively, after heating at 60 °C. The driving force of alloying between Pd shells and Ag atoms was attributed to the distortion of Pd layers over Au NRs based on peak shifts and broadening of XRD data. The higher Ag content in dumbbell-type Au@PdAg NRs was explained by the greater distortion of Pd shells over Au NRs. When the Ag content exceeds its maximum solubility in Pd shells, the third Ag shells were grown over Au@PdAg NRs. For cuboid Au@PdAg NRs, the crystal growth of Ag shells over cuboid Au@PdAg cores begins with the formation of single nuclei on a wide side PdAg alloy facet, followed by growth to one cuboid rod shell and further growth of one or two neighboring cuboid rod shells having {100} facets. On the other hand, for dumbbell-type Au@Pd NRs, Ag shells were deposited over concave curvature of the side facets of Au@PdAg and cuboid Au@PdAg@Ag NRs having one large cuboid Ag block was finally formed in each particle. Our study provides a new simple technique for the epitaxial growth of uniform PdAg alloy layers using spontaneous alloying between Pd shells and Ag atoms over Au NRs.

DOI： 10.1021/jp509340s

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructural changes, such as the density of grain boundary (GB) and dislocation density, due to isochronal annealing in severely plastic-deformed commercial purity aluminium up to 523 K was evaluated using electrical resistivity measurements and scanning transmission electron microscopy. Eventually, the GB density decreases from about 7.2 × 10⁶ to about 2 × 10⁶ m^-1, whilst the dislocation density decreases from an initial value of around 1.3 × 10¹⁴ m^-2 down to around 4 × 10¹³ m^-2.

DOI： 10.1080/14786435.2015.1021400

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Morphological and directional alteration of cells is essential for structurally appropriate construction of tissues and organs. In particular, osteoblast alignment is crucial for the realization of anisotropic bone tissue microstructure. In this article, the orientation of a collagen/apatite extracellular matrix (ECM) was established by controlling osteoblast alignment using a surface geometry with nanometer-sized periodicity induced by laser ablation. Laser irradiation induced self-organized periodic structures (laser-induced periodic surface structures; LIPSS) with a spatial period equal to the wavelength of the incident laser on the surface of biomedical alloys of Ti-6Al-4V and Co-Cr-Mo. Osteoblast orientation was successfully induced parallel to the grating structure. Notably, both the fibrous orientation of the secreted collagen matrix and the c-axis of the produced apatite crystals were orientated orthogonal to the cell direction. To the best of our knowledge, this is the first report demonstrating that bone tissue anisotropy is controllable, including the characteristic organization of a collagen/apatite composite orthogonal to the osteoblast orientation, by controlling the cell alignment using periodic surface geometry.

DOI： 10.1016/j.biomaterials.2014.10.025

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Gd_2-xEu_xO₃ nanophosphor with enhanced luminescence has been synthesized by solution combustion method in diethylene glycol medium. The effect of Eu³⁺ content on the structure, morphology and luminescence dynamics has been investigated. The observed red shift in charge transfer band of the nanophosphor with increase in Eu³⁺content is attributed to the increase in covalency and Eu-O bond length. Excess europium content leads to reduction in intensity of photoemission as a result of concentration quenching. Transient characteristics exhibit single exponential behaviour and the fitted life time values get shortened with increase of Eu³⁺ content, due to increase in non-radiative transition rate. The observed quenching of luminescence in the phosphor is found to be in agreement with the energy transfer theory proposed by Dexter and Schulman and found that dipole-dipole interaction between Eu³⁺ ions is the key mechanism responsible for quenching. Critical energy transfer distance between Eu³⁺ ions in Gd_2-xEu_xO₃ is determined to be 1.148 nm. Judd-Ofelt intensity parameters and the radiative parameters of the phosphors were evaluated from the emission spectrum to analyse the crystal field environment and the degree of covalency between the rare-earth ion and the surrounding ligands. The value of Ω₂ intensity parameter confirmed the hypersensitive nature of the ⁵D₀-⁷F₂ transition with larger asymmetry around Eu³⁺ ions.

DOI： 10.1016/j.ceramint.2015.01.051

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Tensile tests and microstructural observations were carried out to investigate the influence of aging products on tensile deformation behavior of Al-0.62 mass%Mg-0.32 mass%Si alloy. Solution-treated alloys were aged to form needle-like β" precipitates or Mg-Si clusters. The aged alloy with β" precipitates showed higher yield stress than that with Mg-Si clusters. Transmission electron microscopy observations revealed that the β" precipitates pinned dislocations. It was suggested that the strengthening types of the alloy with β" precipitates were both Orowan and cutting mechanism, by estimating the Orowan stress and considering crystal structure of β" precipitates. In contrast, the aged alloys with Mg-Si clusters showed excellent performance of uniform elongation due to large work hardening compared to those of the alloy with β" precipitates. Dislocations in the alloy with Mg-Si clusters were wavy in morphology. The yield stress of the alloy with Mg-Si clusters was higher than that of the solution-treated alloy and much lower than the estimated Orowan stress. This result indicated that the cutting mechanism was the main strengthening type of the aged alloy with Mg-Si clusters, and this strengthening mechanism gave a good balance of strength and elongation.

DOI： 10.2320/jinstmet.J2014063

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Tensile properties of Al-Mg-Si alloy with Mg-Si clusters was compared with that withβ precipitate with the same strength. It was found that the elongation of the alloy with Mg-Si cluster was greater than the alloy with β precipitate because of high work hardening rate, in particular at large strain region. Decomposition of Mg-Si cluster into solute Mg and Si atoms during the tensile deformation test were also shown by differential scanning calorimetry (DSC). Three types of dislocation characteristics were observed from these alloys by transmission electron microscopy (TEM), homogeneous distribution of dislocation with β precipitate, cell structure with Mg and Si in solid solution, and combination of them with Mg-Si cluster. For the case of alloy with Mg-Si cluster, the yield strength was significantly increased due to the cutting mechanism. Simultaneously, the elongation was greatly improved due to the presences of decomposed solute Mg and Si atoms with plastic strain, which are inferred to prevent dynamic recovery in the later stage of tensile test. Consequently, the alloy with clusters has advantages from both alloys with precipitates and solutes, in terms of strength and elongation balance among the conventional 6000 series and 7000 series Al alloys.

DOI： 10.2320/jinstmet.J2015026

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Hydrogen embrittlement has become a crucial issue with the promotion of high-strength steel. As-drawn pearlitic steel wire is well known to have superior resistance to hydrogen embrittlement. The resistance to hydrogen embrittlement is clarified as being further improved by aging treatment at 100-°C and 300-°C for 10-min. of as-drawn 0.8 mass% C pearlitic steel wire with φ5.0 mm (ε=1.9). The higher the aging temperature is, the better the resistance to hydrogen embrittlement becomes. Simultaneously, the strength even increased slightly by aging treatment. The mechanism is investigated by exploiting thermal desorption analysis (TDA) and the newly developed TEM precession analysis. Aging at 100-°C led to a decrease in the hydrogen content at peak I around 100-°C in the TDA curve, which is inferred to be caused by C segregation to dislocations resulting in improvement of hydrogen embrittlement. Aging at 300-°C further improved the resistance to hydrogen embrittlement, which is presumably brought about by the local recovery of the heterogeneously deformed lamellar ferrite area together with the C segregation to dislocations. Here, the strength increased slightly by aging due to the softening factor of recovery and the hardening factor of strain aging.

DOI： 10.2355/tetsutohagane.101.59

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have developed a newly designed straining specimen holder for in situ transmission electron microscopy (TEM) compatible with high-angle single tilt-axis electron tomography. The holder can deform a TEM specimen under tensile stress with the strain rate between 1.5 × 10⁻⁶ and 5.2 × 10⁻³ s⁻¹. We have also confirmed that the maximum tilt angle of the specimen holder reaches ±60° with a rectangular shape aluminum specimen. The new specimen holder, termed as ‘straining and tomography holder’, will have wide range potential applications in materials science.

DOI： 10.1093/jmicro/dfv021

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The majority of engineering steels are ferromagnetic and structurally inhomogeneous on scales ranging from nanometers to micrometers, and their physical properties depend on the three-dimensional (3D) features in their microstructures. Thus, obtaining a 3D image with a large field of view is desirable for transmission electron microscopy (TEM) based microstructure characterization in order to establish the relationship between the microstructure and the physical properties with a reasonable statistical relevancy. Here, we use a conventional sample preparation process, i.e., mechanical polishing followed by electropolishing, and optimizing experimental protocols for electron tomography (ET) of ferromagnetic materials, to carry out microstructural characterization of engineering steel. We determined that the sample thickness after the mechanical polishing step is a critical experimental parameter affecting the success rate of tilt-series image acquisitions. For example, for ferritic heat-resistant 9Cr steel, mechanical thinning down to 30 μm or less was necessary to acquire an adequate tilt-series image of the carbide precipitates in the annular dark-field scanning TEM (ADF-STEM) mode. However, acquiring tilt-series images of dislocation structures remains a challenge due to an unavoidable, significant electron beam deflection during specimen tilt, even with a thinned sample. To overcome the electron beam deflection problem, we evaluated several relatively accessible approaches including the "Low-Mag STEM and Lorentz TEM" modes. Although rarely used for ET, both modes reduce or even zero the objective lens current, likely weakening the magnetic interference between the ferromagnetic specimen and the objective lens magnetic field. The advantages and disadvantages of these experimental components are discussed.

DOI： 10.2355/isijinternational.55.623

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Codeposition of metal chlorides with Pt colloidal nanoparticles on TiO₂ followed by oxidation at 400 °C and reduction at 200 °C improved the activity for Pt-catalyzed CO oxidation with stoichiometric amount of O₂. The highest activity was obtained when FeCl₃ was used as the additive with the Fe/Pt ratio of 0.2. XAFS, X-EDS, FTIR, and catalytic studies revealed that the deposition of Fe species on the reduced Pt sites gave active sites, which exhibited CO oxidation with high efficiency.

DOI： 10.1246/cl.150903

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The present authors recently developed a time-dependent Ginzburg-Landau (TDGL) formulation for ordering processes of B2 and D0³ in binary alloys, taking into account the symmetrical relationships between these ordered phases. Kinetic equations for time-evolution of order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of a mean-field free energies and interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. Micro-structures in the superalloys consist of B2 ordered domains and A2 disordered matrices in the first stage of phase separation. The second stage during a subsequent aging leads to formation of B2 domains and A2 phase regions in the former A2 matrices and B2 domains, respectively. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors have applied the TDGL formulation to this alloy system, and performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigated the improvement in magnetic properties of high-purity Fe-(5, 6) wt% Si formed by cold crucible levitation melting. The results showed that Fe-6 wt% Si alloy has a smaller coercivity than Fe-5 wt% Si. The hysteresis loss of both alloys increases linearly and slightly with maximum magnetization, and increases significantly after a certain maximum magnetization. Additionally, demagnetized domain structure and domain wall motion in both samples was studied by means of Lorentz microscopy. The results indicated that the domain wall motion of Fe-6 wt% Si can be activated in lower external fields and displaces more rapidly than Fe-5 wt% Si. Moreover, the displacement of domain walls that penetrate symmetrical grain boundaries and dislocations in Fe-6 wt% Si was analyzed. The boundaries and dislocations have no pinning effect on domain wall motion.

DOI： 10.1016/j.phpro.2015.12.090

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this work, we report first-principles investigation of structural stability of all experimentally observed ordered long-period superstructures (LPSs), viz., r-Al₂Ti, h-Al₂Ti, Al₅Ti ₃ along with Al₅Ti₃′, Al ₁₁Ti₇ and Al₃Ti₂ LPSs, which are observed only as short-range ordered clusters at nanoscale level in Al-rich TiAl-based alloys. We adopt a procedure based on space-filling tiling arrangement of ordered Ti₂Al, Ti₃Al, Ti₄Al motifs and their combination along with a symmetry analysis programme to determine the unit cell and the crystallographic information of Al ₅Ti₃′, Al₁₁Ti₇ and Al ₃Ti₂ LPSs in terms of L₁₀ fcc unit cell. First-principles calculations are performed to further refine these crystallographic parameters (Wyckoff positions and lattice parameters) obtained from the above procedure. Moreover, it is found that the family of five LPSs have subgroup-supergroup relationships with γ-TiAl (Sp. gr. P4/mmm) and among themselves. Further, we find the inherent stability of r-Al₂Ti + γ-TiAl and 2Al₅Ti₃ + γ-TiAl phase mixtures at 0 K compared to isomolecular Al₃Ti₂ and Al ₁₁Ti₇ LPSs at their respective concentrations. The calculations of single-crystal elastic constants of Al₅Ti ₃, Al₁₁Ti₇, Al₃Ti₂ and Al₅Ti₃′ LPSs show all these four structures are mechanically stable. We also calculate antiphase boundary (APB) formation energies for two types of APBs, viz., type-A and type-C in ordered Al ₅Ti₃ LPS using the supercell approach. The relaxed APB energies for type-A and type-C APBs are 15.44 and 124.16 mJ/m², respectively.

DOI： 10.1080/14786435.2014.885135

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this work, we report first-principles investigation of structural stability of all experimentally observed ordered long-period superstructures (LPSs), viz., r-Al2Ti, h-Al2Ti, Al5Ti3along with Al5Ti3′, Al11Ti7and Al3Ti2LPSs, which are observed only as short-range ordered clusters at nanoscale level in Al-rich TiAl-based alloys. We adopt a procedure based on space-filling tiling arrangement of ordered Ti2Al, Ti3Al, Ti4Al motifs and their combination along with a symmetry analysis programme to determine the unit cell and the crystallographic information of Al5Ti3′, Al11Ti7and Al3Ti2LPSs in terms of L10fcc unit cell. First-principles calculations are performed to further refine these crystallographic parameters (Wyckoff positions and lattice parameters) obtained from the above procedure. Moreover, it is found that the family of five LPSs have subgroup-supergroup relationships with γ-TiAl (Sp. gr. P4/mmm) and among themselves. Further, we find the inherent stability of r-Al2Ti + γ-TiAl and 2Al5Ti3+ γ-TiAl phase mixtures at 0 K compared to isomolecular Al3Ti2and Al11Ti7LPSs at their respective concentrations. The calculations of single-crystal elastic constants of Al5Ti3, Al11Ti7, Al3Ti2and Al5Ti3′ LPSs show all these four structures are mechanically stable. We also calculate antiphase boundary (APB) formation energies for two types of APBs, viz., type-A and type-C in ordered Al5Ti3LPS using the supercell approach. The relaxed APB energies for type-A and type-C APBs are 15.44 and 124.16 mJ/m2, respectively. © 2014 Taylor and Francis.

DOI： 10.1080/14786435.2014.885135

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The solvothermal synthesis of highly luminescent and homogeneous Gd ₂O₃:Eu³⁺ nanophosphor using diethylene glycol as medium, followed by controlled combustion with citric acid as fuel is reported. The influence of concentrations of carboxylic acid and metal cations on the structure, morphology and luminescence properties are investigated in detail. The microscopic investigations indicate the nanocrystalline nature and the strong influence of cation concentration on the size, shape and agglomeration of the particles. It is found that increase in concentration of metal cations lead to the reduction in agglomeration of nanophosphors. The large value of intensity parameter Ω_2, suggested that Eu ³⁺ ions reside in a more asymmetric environment, resulted in intense emission due to ⁵D₀-⁷F₂ electric dipole transition. Emission decay analysis of the samples exhibited one exponential nature. The samples prepared under optimum conditions showed a quantum efficiency of 78.63% and a moderately high life time of 1.217 ms.

DOI： 10.1016/j.ceramint.2013.10.020

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We measured a creep deformation in Grade T91 steel under low stress condition using a helicoid spring creep test method. By applying this method, we measured a very low strain rate creep deformation in a short time as there is no need to consider the contribution of the microstructural change to the creep deformation behavior. We distinguished magnitude of several types of time-dependent deformation, including viscoelastic deformation, which occurs during the creep test in order to evaluate a time-dependent plastic deformation in strain-time curves. This consideration derives a conclusion that the time-dependent plastic deformation occurs even in a short time and low stress condition. Moreover, we confrmed a strain rate of whole creep deformation is controlled by the strain rate of the time-dependent plastic deformation at the time of 270 ks in the creep test. We confrmed that though there are almost no changes in the microstructure of Grade T91 steel during creep tests, the susceptibility on strain rate to applied stress has changed depending on the applied stress region. In addition, activation energy of the creep deformation was also different in each stress region. From these results, we concluded that the dominant creep deformation mechanism is different in the low stress region and high stress region.

DOI： 10.2355/tetsutohagane.100.688

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A comprehensive study of the effects of structural imperfections in MgB₂ superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB₂ material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB₂, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB₂, however, even at low sintering temperature, and thus block current transport paths.

DOI： 10.1063/1.4862670

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In previous studies, the secondary (impurity and non-reactive) phase and voids were observed in MgB₂ matrix after the heat treatment, and then these are the lowering factors of critical current density (J_c) property. In order to improve J_c property by microstructure control of MgB₂ matrix, the fine elemental boron powder as the raw material was carried out using the high-speed vibrated milling with tungsten carbide (WC) jar. The average particle size of metal boron powder was decreased from 1.14 μm to 0.20 μm by the high-speed vibrated milling. The various fine particle boron powders as the function of milling time were also prepared, and in-situ Cu addition MgB₂ multifilamentary wires using these fine boron powders were fabricated. Critical transition temperature (T_c) value of Cu addition MgB₂ wire using fine boron powder obtained to about 37 K. No change of the T_c property by the different particle sized boron powders was confirmed. In this paper, the comparisons of microstructure and superconducting properties between the different boron particle sizes were investigated.

DOI： 10.1088/1742-6596/507/2/022009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The transition of the creep deformation mechanism in the low-stress region of Grade P92 high Cr ferritic heat-resistant steel was investigated by a helicoid spring creep test. Specifically, the effect of variation in the microstructure of steel on creep deformation behavior was evaluated by subjecting samples to thermal aging for 1000, 3000, 5000, and 10000 h at 700°C over a wide stress range. In addition, stress exponents were determined from the stress dependence of the minimum strain rate in the creep curves up to 270 ks. The transition of the creep mechanism was indicated when the stress exponent decreased from 4 in the high-stress region to 1 in the low-stress region below 40 MPa. A quantitative evaluation of the microstructure of a tempered martensite sample, including the determination of the amount of dissolved Mo and W, dispersion state of the precipitates, and length of the grain boundaries per unit area, was also carried out. Furthermore, the change in the minimum strain rate was evaluated as a function of the microstructural changes that accompanied thermal aging. It was found that the change in the strain rate was the most affected by the fineness of the martensitic lath structure in the high-stress region and by the dispersion density of M23C6 precipitates in the low-stress region. Based on these results, it was concluded that the microstructural parameter that most affects creep deformation behavior differs depending on the stress region due to the difference in the creep mechanism.

DOI： 10.2320/matertrans.M2013427

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Gd_1.9Eu_0.1O₃ nanophosphor with enhanced photoemission is successfully synthesized by a controlled combustion method of metal-citrate complex in diethylene glycol medium. It is found that the phase formation and spectral properties including quantum efficiency are highly sensitive to sintering temperature and the role of citric acid both as a chelating agent and as a fuel for combustion was evident in the study. The formation of cubic Gd₂O₃:Eu nanocrystalline phosphor was confirmed by X-ray diffraction, Raman and Infrared measurements. Transmission electron microscopic images together with the SAED patterns indicate the formation of spherical Gd₂O₃ nanocrystalline powder with well defined planes separated by 0.312 nm of cubic Gd₂O₃. The high degrees of homogeneity observed in the electron micrographs are attributed to the glycol medium used. The intensities of transitions between different J levels depend on the symmetry of the local environment of Eu ³⁺ activators and are described using the Judd-Ofelt analysis. The spectral properties of the samples prepared under optimum conditions have shown large asymmetric ratio, indicating high degree of distortion in local environment around Eu³⁺ ions and a maximum quantum efficiency of 78% was obtained. The life-time measurements indicated an increase from 0.83 to 1.28 ms with increase in sintering temperature from 700 to 1000 C. The chromaticity and correlated colour temperature of the emission were evaluated based on the 1931 CIE chromaticity diagram. The absorptions observed in the excitation spectra show the suitability of the nanophosphor obtained in this study for getting excited in UV, NUV and visible regions for a variety of device applications.

DOI： 10.1016/j.ceramint.2013.05.010

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Instantaneous creep in face-centered cubic metals, 5N Al (99.999%), 2N Al (99%) and 4N Cu (99.99%) with different grain sizes, was firstly investigated by sudden stress-change experiments at ultralow strain rates dot \varepsilon ≤ 10^-10 s^-1 and temperature T < 0.32 T _m. The experimental results indicate that the observed instantaneous creep is strongly dependent on grain size, the concentration of impurity, and stacking fault energy. Creep in high-purity aluminum, 5N Al, with a very large grain size, d _g > 1600 μm, shows non-viscous behavior, and is controlled by the recovery of dislocations in the boundary of dislocation cells. On the other hand, for 5N Al with a small grain size, d _g=30 μm, and low-purity aluminum, 2N Al, with d _g= 25 μm, creep shows viscous behavior and may be related to 'low temperature grain boundary sliding'. For high-purity copper, 4N Cu, with d _g= 40 μm and lower stacking fault energy, creep shows a non-viscous behavior, and is controlled by the recovery process of dislocations. For all of the samples, creep shows anelastic behavior.

DOI： 10.1007/s11595-013-0826-y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Europium-doped strontium aluminate [SrAl₂O₄:Eu ²⁺] (SAOE) emits green light under an applied mechanical stress in a phenomenon called mechanoluminescence (ML). In order to clarify the relationship between ML and its structure, the microstructure, phase transformation behavior and structural change under a load on SAO ceramics were investigated. The microstructures were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been that SAO has a twin structure with three kinds of morphologies. The phase transformation behavior was investigated using differential scanning calorimetric (DSC) measurements and observation of the microstructures. It is indicated that the twin structures are formed by a thermoelastic martensitic transformation from a hexagonal (β) to a monoclinic (α) phase at about 670 C. In addition, the structural change under a load was observed by in situ TEM nanoindentation. It is clarified that pseudoelastic deformation occurred in SAO. These results suggest that ML occurs with rearrangement of variants of α phase. Crown

DOI： 10.1016/j.jallcom.2012.04.009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures and hardness of a Fe-1.4%Cr-1%C pearlitic steel processed by super-rapid induction heating-and-quenching (SRIHQ) under various conditions have been investigated. A nano-scaled laminated microstructure composed of two different types of martensite (highly-twinned or containing a high dislocation density) was formed and the maximum hardness was obtained by heating to 1223. K in 0.5. s and quenched. Electron energy loss spectroscopy indicated that the two different types of martensite were formed depending on the local solute-concentration in the non-uniform solute-distribution realized by the SRIHQ-process.

DOI： 10.1016/j.msea.2013.04.024

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Transient creep at very low strain rates (less than 10^-10s ^-1) is still unclear. The traditional uniaxial creep testing is less useful due to unsatisfied resolution strain ∼(10^-6). To study transient creep behavior at such low strain rates, a high-resolution strain measurement using the helicoid spring specimen technique was employed in a fine-grained Al-5356 alloy at temperatures ranging from 0.47 T_m to 0.74T_m (T_m: melting point). To clarify transient creep mechanism at such low strain rates, transmission electron microscopy (TEM) was used in microstructure observation of crept specimens. The abnormal transient creep, high temperature strengthening at T>T_p(T_p: the phase transformation temperature, 0.58T_m) or intermediate temperature softening at 0.4T_m<T≤T_p and double-normal type (creep curves including double work-hardening stages) at T=T_p, were firstly observed. The substructure observation in a crept specimen at T=0.58T_m and É=1*10^-4 shows pile-up dislocations including many small jogs with equal interval, and dislocations emitted from grain boundaries. The β-Al₃Mg₂ phase dissolves under the condition of testing temperatures higher than 523 K, which causes solid-solution quantity of Mg atoms to increase. Therefore, the "abnormal transient creep" may be related to the difference of solid solution strengthening caused by phase change during the creep tests.

DOI： 10.1016/S1003-6326(13)62585-6

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Research on the MgB2/Ni and MgB2/B multilayer films fabricated by an electron beam (EB) evaporation technique have been extensively carried out. The critical current density, J(c) of MgB2/Ni and MgB2/B multilayer films in parallel fields has been suggested to be higher than that of monolayer MgB2 film due to introducing the artificial pinning centers of nano-sized Ni and B layers. Nanostructure characterization of the artificial pinning centers in the multilayer films were examined by transmission electron microscopy (TEM) and scanning TEM (STEM-energy dispersive X-ray spectroscopy (STEM-EDS))-EDS to understand the mechanism of flux pinning. The growth of columnar MgB2 grains along the film-thickness direction was recognized in the MgB2/Ni multilayer film, but not in the MgB2/B multilayer film. Nano-sized Ni layers were present as crystalline epitaxial layers which is interpreted that Ni atoms might be incorporated into the MgB2 lattice to form (Mg, Ni)B-2 phase. On the other hand, nano-sized B layers were amorphous layers. Crystalline (Mg, Ni) B-2 layers worked more effectively than amorphous B-layers, providing higher flux-pinning force that resulted in higher J(c) of the MgB2/Ni multilayer film than the MgB2/B multilayer film. (C) 2013 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.physc.2013.02.011

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report a first-principles study of the phase stability and electronic structure of tetragonal (P4/m) Ga-3 (x) Al (x) Ti-2 (x=03) compounds to investigate the conspicuous absence of Al3Ti2 in the AlTi phase diagram while isostructural Ga3Ti2 is stable in the GaTi phase diagram. It is found that Ga3Ti2 is the most stable phase compared to its ternary derivatives (Ga-3 (x) Al (x) )Ti-2, with the stability of Al3Ti2 being the lowest. Furthermore, the equimolecular phase mixture of -TiAl and r-Al2Ti is found to be more stable than Al3Ti2. By analysing the total and partial density of states, the valence charge transfer and the valence charge density distributions, we substantiate our conclusions from the perspective of the electronic structure.

DOI： 10.1080/09500839.2013.769068

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Research on the MgB₂/Ni and MgB₂/B multilayer films fabricated by an electron beam (EB) evaporation technique have been extensively carried out. The critical current density, J_c of MgB₂/Ni and MgB₂/B multilayer films in parallel fields has been suggested to be higher than that of monolayer MgB₂ film due to introducing the artificial pinning centers of nano-sized Ni and B layers. Nanostructure characterization of the artificial pinning centers in the multilayer films were examined by transmission electron microscopy (TEM) and scanning TEM (STEM-energy dispersive X-ray spectroscopy (STEM-EDS))-EDS to understand the mechanism of flux pinning. The growth of columnar MgB₂ grains along the film-thickness direction was recognized in the MgB₂/Ni multilayer film, but not in the MgB₂/B multilayer film. Nano-sized Ni layers were present as crystalline epitaxial layers which is interpreted that Ni atoms might be incorporated into the MgB₂ lattice to form (Mg,Ni)B ₂ phase. On the other hand, nano-sized B layers were amorphous layers. Crystalline (Mg,Ni)B₂ layers worked more effectively than amorphous B-layers, providing higher flux-pinning force that resulted in higher J_c of the MgB₂/Ni multilayer film than the MgB ₂/B multilayer film.

DOI： 10.1016/j.physc.2013.02.011

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report a first-principles study of the phase stability and electronic structure of tetragonal (P4/m) Ga3-x Al x Ti2 (x = 0-3) compounds to investigate the conspicuous absence of Al3Ti2 in the Al-Ti phase diagram while isostructural Ga3Ti2 is stable in the Ga-Ti phase diagram. It is found that Ga3Ti2 is the most stable phase compared to its ternary derivatives (Ga3-x Al x)Ti2, with the stability of Al3Ti2 being the lowest. Furthermore, the equimolecular phase mixture of γ-TiAl and r-Al2Ti is found to be more stable than Al3Ti2. By analysing the total and partial density of states, the valence charge transfer and the valence charge density distributions, we substantiate our conclusions from the perspective of the electronic structure.

DOI： 10.1080/09500839.2013.769068

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Formation of domain structures in two-step phase separation in Fe-based Fe-Ni-Al alloys are investigated by applying a time-dependent Ginzburg-Landau (TDGL) model. The present authors recently developed a TDGL formulation for ordering processes of B2 and D0₃ in binary alloys, taking into account the symmetrical relationships between these ordered phases. In this formulation, multiple types of variants of the structures are represented by three order parameters which can be measured independently through crystal structure factors. Mean-field free energies are defined in a form of Landau type expansion with the order parameters and a composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations.

DOI： 10.1557/opl.2013.456

記述言語：英語   掲載種別：研究論文（学術雑誌）  

MgB2 is a promising superconductor for future applications to superconduct wires and tapes used at the liquid hydrogen temperature (20 K). Because the maximal superconducting current (critical current) in MgB 2 depends on its microstructure, an "in-situ" process to fabricate MgB2 based on a reaction between Mg and B is effective in controlling the microstructure. However, the critical current in the fabricated MgB2 wires and tapes is not sufficiently high for practical use. This may be attributed to the imperfectness of the microstructural control in MgB2 wires and tapes. In this paper, we will discuss the microstructural features of MgB2 tapes fabricated using a typical in-situ powder-in-tube process. By observing the early stage of microstructural evolution in detail, we can gain insights into the next strategy for improving the microstructure of MgB2 tapes with respect to their applications. © 2012 Springer Science+Business Media New York.

DOI： 10.1007/s10853-012-6901-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Long-period ordered superstructures in an (Al,Ga)-rich (Al,Ga)Ti system composed of (Al,Ga)_x Ti_100-x (x = 50-65 at. %) were investigated by using melt-spun ribbons, focusing on the ordering process of the superstructural phases. Compositional regions in which h-(Al,Ga)₂Ti (Ga₂Zr-type), (Al,Ga)₅Ti₃ and (Al,Ga) ₃Ti₂ with threefold, fourfold and fivefold periodicity, respectively, appeared coherently in the L1₀ matrix were identified by electron diffraction patterns in two different temperature conditions of as-spun (a relatively high-temperature state) and heat-treatment at 700°C (a relatively low-temperature state). The (Al,Ga)₅Ti₃ superstructural phase always existed between the compositional region where h-(Al,Ga)₂Ti and (Al,Ga)₃Ti₂ dominantly appear. Therefore, periodical ordering proceeds following the periodicity of the concentration wave of pure (Al,Ga) layers parallel to {310) in the Ti (002) layers from threefold to fivefold periodicity via fourfold periodicity. We found that the (Al,Ga)₃Ti₂ long-period superstructural phase preferentially appeared with increasing Ga concentration in the melt-spun ribbon annealed at 700°C. In other words, the h-(Al,Ga)₂Ti superstructure with threefold periodicity preferentially appeared at the high temperature and a low Ga concentration. Thus, the (Al,Ga)₃Ti ₂-type superstructure was never produced without the addition of Ga in the present study. The long-period ordered superstructures were composed of three pairs of primitive cells, (Al,Ga)Ti₂, (Al,Ga)Ti₃ and (Al,Ga)Ti₄, with periodic atomic arrangements corresponding to lean rhombus, fat rhombus and square, respectively. We discuss the ordering process throughout the (Al,Ga)₅ superstructure based on the periodic concentration wave and exchange of atoms. The effect of long-period ordered superstructures on hardness is also mentioned.

DOI： 10.1080/14786435.2012.699691

記述言語：英語   掲載種別：研究論文（学術雑誌）  

MgB₂ is a promising superconductor for future applications to superconduct wires and tapes used at the liquid hydrogen temperature (20 K). Because the maximal superconducting current (critical current) in MgB ₂ depends on its microstructure, an "in-situ" process to fabricate MgB₂ based on a reaction between Mg and B is effective in controlling the microstructure. However, the critical current in the fabricated MgB₂ wires and tapes is not sufficiently high for practical use. This may be attributed to the imperfectness of the microstructural control in MgB₂ wires and tapes. In this paper, we will discuss the microstructural features of MgB₂ tapes fabricated using a typical in-situ powder-in-tube process. By observing the early stage of microstructural evolution in detail, we can gain insights into the next strategy for improving the microstructure of MgB₂ tapes with respect to their applications.

DOI： 10.1007/s10853-012-6901-5

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The creep deformation in pure aluminum was investigated using helicoid spring samples at room temperature, 298 K, and σ < 1.19 MPa. It was found that the stress exponent is n = 0, which means the creep behavior in this region is independent on applied stress but some physical properties of materials. The creep behavior was suggested to be controlled by surface diffusion based on the strongly effect of surface area on creep behavior only in this creep region (n = 0). The threshold creep rate, th ∑_th, called "intrinsic deformation limit", decided by surface diffusion was suggested. This discovery provided a new perspective to understand the extremely slow deformation in the nature.

DOI： 10.4028/www.scientific.net/MSF.747-748.559

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigated the microstructures and superconducting properties of Bi,Pb-2223 thin films on SrTiO₃(100) fabricated by radio-frequency (RF) sputtering and annealing. Most as-deposited films fabricated by RF sputtering did not exhibit a superconducting transition due to their low crystallinity, their deviation from the composition of Bi-2223, and their low intergrain connectivity. The as-deposited films did not contain Pb. To obtain the Bi,Pb-2223 phase, we annealed the film with Bi,Pb-2223 pellets and powder. After annealing, we confirmed that the thin film contained Pb. T _c
^zero = 100 K was obtained in Bi,Pb-2223 thin film after post-annealing. We observed strong 00l peaks and a sharp quadrupole in X-ray θ - 2θ and φ-scan measurements. These results suggest that this film consists of a single phase of Bi,Pb-2223 and has a biaxial orientation. The Bi,Pb-2223 thin film had a maximum J_c of 0.1 × 10 ⁵A/cm² at 78 K in a magnetic field of 2 T. Furthermore, Bi,Pb-2223 exhibited very strong anisotropy in its J_c-B angle characteristics.

DOI： 10.1109/TASC.2012.2233856

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The present authors recently developed a time-dependent Ginzburg-Landau (TDGL) formulation for ordering processes of B2 and D0₃ in binary alloys, taking into account the symmetrical relationships between these ordered phases. In this formulation, mean-field free energies are defined in a form of Landau type expansion with order parameters and a composition parameter. Interfacial energies due to local variations of degrees of order and composition are given in a gradient square approximation. Kinetic equations for time-evolution of the order parameters and the composition one are derived from the Ginzburg-Landau type potential consisting of the mean-field free energies and the interfacial energy terms. On the other hand, coauthors have investigated domain structures in two-step phase separation of Fe-based Fe-Ni-Al alloys. Micro-structures in the super alloys consist of B2 ordered domains and A2 disordered matrices in the first stage of phase separation. The second stage during a subsequent aging leads to formation of B2 domains and A2 phase regions in the former A2 matrices and B2 domains, respectively. The evolution of three-dimensional domain structures and composition profiles has been analyzed by electron tomography imaging and energy-dispersive X-ray spectroscopy. In this work the authors have applied the TDGL formulation to this alloy system, and performed three-dimensional numerical simulations assuming the thermal processing. The results of the simulations well reproduced the characteristics of the micro-structures obtained from the observations.

DOI： 10.1063/1.4794662

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The metal Al is lighter in weight than other substrate materials for MgB₂ films such as Si and Ni. This property inspires MgB₂ fabrication on a large-scale Al substrate as a new route to MgB₂ tapes. Here we report microstructural factors influencing critical current density, J_c, in MgB₂/Al films. MgB₂/Al films were prepared by the following steps: deposit a boron layer of 3 nm in thickness on an Al substrate heated at 280°C ; deposit Mg and boron on the boron layer (sample A). For comparison, Mg and boron were deposited directly on an Al substrate heated at 265°C (sample B). The microstructure was observed by transmission electron microscopy (TEM) and scanning TEM. J_c values at 20 K in the self-field were 4.9 × 10⁶ A cm^-2 for sample A and 2.7 × 10⁶ A cm^-2 for sample B. Both the samples form an oxygen-rich layer of 10 nm in thickness at the substrate surface. This oxygen-rich layer may suppress Al diffusion into MgB₂ lattices. The [001] texture of columnar MgB₂ crystals grown on the substrate is stronger in sample A than in sample B. This indicates that the boron layer deposition on the Al substrate is effective for fabricating well-textured MgB₂ polycrystals, resulting in the higher J _c enhancement for sample A.

DOI： 10.1109/TASC.2013.2238284

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In order to study the mechanism of phase transformation from Bi-2212 to Bi-2223, we fabricated Pb-Ca-Cu deposited Bi-2212 (001) single crystals as precursors of the Bi,Pb-2223 phase. These single crystals were heated in a sintered Bi-Pb-Sr-Ca-Cu-O pellet, and microstructure was observed by analytical electron microscopy. As a result of the microstructural observation around the Bi,Pb-2223 phase, two formation paths of Bi,Pb-2223 were recognized. One is the formation from a liquid phase which is formed by Bi-2212 and melting of the secondary phases such as (Ca,Sr)₂PbO₄ and CuO. The other is the growth of Bi,Pb-2223 into Bi-2212 phase by diffusion of Pb, Ca and Cu atoms along the 〈hk0〉 directions of Bi-2212.

DOI： 10.1016/j.phpro.2013.04.054

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

We review the progress in the electron tomography of dislocation microstructures in the transmission electron microscope (TEM). Dislocation contrast is visible both in conventional TEM and scanning TEM (STEM) modes and, despite the complicated intensity variations, dislocation contrast can be isolated using computational filtering techniques prior to reconstruction. We find that STEM annular dark-field (STEM-ADF) imaging offers significant advantages in terms of dislocation contrast and background artifacts. We present several examples, both in semiconducting and metallic systems, illustrating the properties of 3D dislocations. We present the high-angle triple-axis (HATA) specimen holder where the diffraction condition can be chosen at will and dislocation tomograms of multiple reflections can be combined. 3D dislocations are analyzed in terms of dislocation density and dislocation nodal structures. Several avenues of study are suggested that may exploit the 3D dislocation data.

DOI： 10.1557/opl.2012.430

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Premonitory effects manifest themselves in an ordering transition of the first kind (order) in the form of anomalously high short-range order (SRO) intensity at temperatures marginally above Tc, the critical transition temperature. This intensity located at the superlattice positions of the long-range ordered (LRO) phase is often attributed to the formation of ‘heterophase fluctuations’ resembling clusters of the LRO phase. Monte Carlo simulations in a hypothetical system showing FCC-to-L12ordering transition have been carried out here to shed some light on this phenomenon and to look into the atomic configurations that make up these fluctuations. 92. © 1997, Taylor & Francis Group, LLC. All rights reserved.

DOI： 10.1080/14786435.2012.713136

記述言語：日本語  

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Creep-rupture tests and Charpy impact tests after long-term thermal aging were performed for three austenitic heat-resistant steels of which compositions were Fe-25%Ni-23.5%Cr-1%Mo-6%W-(0.11 to 0.27)%N-0.05%Ti-0.20%V-0.25%Nb-0.004%B by wt% to reveal the influence of nitrogen contents on the mechanical properties required for boiler tubes. Creep-rupture strengths of the steels at 700 degrees C for 6000 h were higher than 155 MPa. The material which showed the highest strength at 700 degrees C for 6000 h was the 0.21N steel. Nitrogen in the steels contributes to increasing the creep-rupture strength. The effect of nitrogen under higher stress condition became larger while the effect became smaller under lower stress condition. It was supposed that nitrogen decreased the effect of precipitation strengthening by stabilizing the austenite phase for a longer time while it increased the effect of solid solution strengthening. On the other hand, the Charpy impact value of all steels after aging at 700 degrees C for 1000 h became less than 10 J/cm(2). Nitrogen in the steels did not have a notable influence on the toughness after long-term thermal aging because precipitates of M23C6 and a tungsten-rich phase formed along grain boundaries deteriorated the toughness.

DOI： 10.2355/tetsutohagane.98.117

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Increasing dissipation-free supercurrent has been the primary issue for practical application of superconducting wires. For magnesium diboride, MgB ₂, carbon is known to be the most effective dopant to enhance high-field properties. However, the critical role of carbon remains elusive, and also low-field critical current density has not been improved. Here, we have undertaken malic acid doping of MgB₂ and find that the microscopic origin for the enhancement of high-field properties is due to boron vacancies and associated stacking faults, as observed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The carbon from the malic acid almost uniformly encapsulates boron, preventing boron agglomeration and reducing porosity, as observed by three-dimensional X-ray tomography. The critical current density either exceeds or matches that of niobium titanium at 4.2 K. Our findings provide atomic-level insights, which could pave the way to further enhancement of the critical current density of MgB₂ up to the theoretical limit.

DOI： 10.1038/am.2012.3

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Increasing dissipation-free supercurrent has been the primary issue for practical application of superconducting wires. For magnesium diboride, MgB2, carbon is known to be the most effective dopant to enhance high-field properties. However, the critical role of carbon remains elusive, and also low-field critical current density has not been improved. Here, we have undertaken malic acid doping of MgB2 and find that the microscopic origin for the enhancement of high-field properties is due to boron vacancies and associated stacking faults, as observed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The carbon from the malic acid almost uniformly encapsulates boron, preventing boron agglomeration and reducing porosity, as observed by three-dimensional X-ray tomography. The critical current density either exceeds or matches that of niobium titanium at 4.2 K. Our findings provide atomic-level insights, which could pave the way to further enhancement of the critical current density of MgB2 up to the theoretical limit. NPG Asia Materials (2012) 4, e3; doi:10.1038/am.2012.3; published online 18 January 2012

DOI： 10.1038/am.2012.3

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The natural boron has two kinds of isotopes which are existed 20 wt% boron-10 (¹⁰B) and 80 wt% boron-11 (¹¹B). ¹¹B isotope is stable against the neutron irradiation without nuclear transformation. For an advanced fusion application, in-situ PIT process using ¹¹B isotope powder as the boron source material was desirable to enhance low induced radio-activity of MgB₂superconducting wire. We tried to fabricate the in-situ Cu addition MgB2/Ta/Cu multifilamenatry wire using boron isotope powder as the boron source material. In this study, superconductivity and microstructure of MgB₂ wire using boron isotope powder were investigated. Tc value of MgB₂ wire using 11B powder was shown to about 37 K by the low temperature diffusion reaction, and its value was higher than commercial natural powder. However, Jc value of MgB₂ wire using ¹¹B isotope powder was remarkably lower than that of commercial natural powder. This is caused by the forming of much impurity phase and decrease of MgB₂ volume fraction due to the remaining of much non-reactive ¹¹B isotope powder.

DOI： 10.1016/j.phpro.2012.06.119

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Creep-rupture tests and Charpy impact tests after long-term thermal aging were performed for three austenitic heat-resistant steels of which compositions were Fe-25%Ni-23.5%Cr-1%Mo-6%W-(0.11 to 0.27)%N-0.05%Ti-0.20%V-0.25%Nb-0.004%B by wt% to reveal the influence of nitrogen contents on the mechanical properties required for boiler tubes. Creep-rupture strengths of the steels at 700 °C for 6000 h were higher than 155 MPa. The material which showed the highest strength at 700 °C for 6000 h was the 0.21N steel. Nitrogen in the steels contributes to increasing the creep-rupture strength. The effect of nitrogen under higher stress condition became larger while the effect became smaller under lower stress condition. It was supposed that nitrogen decreased the effect of precipitation strengthening by stabilizing the austenite phase for a longer time while it increased the effect of solid solution strengthening. On the other hand, the Charpy impact value of all steels after aging at 700 °C for 1000 h became less than 10 J/cm2. Nitrogen in the steels did not have a notable influence on the toughness after long-term thermal aging because precipitates of M23C6 and a tungsten-rich phase formed along grain boundaries deteriorated the toughness.

DOI： 10.2355/tetsutohagane.98.117

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Various long-period superstructures that appear in Al-rich TiAl are composed of three pairs of primitive cells, Ti ₂Al, Ti ₃Al, and Ti ₄Al, having periodic atomic arrangements in unique shapes of lean rhombi, fat rhombi, and squares, respectively, on the (002) Ti layers. These primitive cells can produce long-period superstructures such as Al ₅Ti ₃, Al ₃Ti ₂, and h-Al ₂Ti. The long-period superstructures play an important role in the operative deformation mode, configuration of dislocations, and related plastic deformation behavior in Al-rich TiAl, depending on the Al concentration. Fourfold ordinary dislocations, for example, often move as a group in the Al ₅Ti ₃ superstructure in the shapes of lean rhombi and squares embedded in the L1 ₀ matrix. In this study, the relationship between the periodic long-period superstructures and dislocation motion will be discussed from the viewpoint of anti-phase boundaries that form in each superstructure and their energies. The plastic deformation behavior in Al ₅Ti ₃ and h-Al ₂Ti single-phase single crystals is also discussed.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Premonitory effects manifest themselves in an ordering transition of the first kind (order) in the form of anomalously high short-range order (SRO) intensity at temperatures marginally above Tc, the critical transition temperature. This intensity located at the superlattice positions of the long-range ordered (LRO) phase is often attributed to the formation of ‘heterophase fluctuations’ resembling clusters of the LRO phase. Monte Carlo simulations in a hypothetical system showing FCC-to-L1₂ ordering transition have been carried out here to shed some light on this phenomenon and to look into the atomic configurations that make up these fluctuations. 92.

DOI： 10.1080/14786435.2012.713136

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Focused ion beam (FIB) induced damage in nanocrystalline Al thin films has been characterized using advanced transmission electron microscopy techniques. Electron tomography was used to analyze the three-dimensional distribution of point defect clusters induced by FIB milling, as well as their interaction with preexisting dislocations generated by internal stresses in the Al films. The atomic structure of interstitial Frank loops induced by irradiation, as well as the core structure of Frank dislocations, has been resolved with aberration-corrected high-resolution annular dark-field scanning TEM. The combination of both techniques constitutes a powerful tool for the study of the intrinsic structural properties of point defect clusters as well as the interaction of these defects with preexisting or deformation dislocations in irradiated bulk or nanostructured materials.

DOI： 10.1017/S143192761101213X

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Focused ion beam (FIB) induced damage in nanocrystalline Al thin films has been characterized using advanced transmission electron microscopy techniques. Electron tomography was used to analyze the three-dimensional distribution of point defect clusters induced by FIB milling, as well as their interaction with preexisting dislocations generated by internal stresses in the Al films. The atomic structure of interstitial Frank loops induced by irradiation, as well as the core structure of Frank dislocations, has been resolved with aberration-corrected high-resolution annular dark-field scanning TEM. The combination of both techniques constitutes a powerful tool for the study of the intrinsic structural properties of point defect clusters as well as the interaction of these defects with preexisting or deformation dislocations in irradiated bulk or nanostructured materials.

DOI： 10.1017/S143192761101213X

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Monotonic creep tests were carried out on fine-grained Al-5356 alloy with grain size d_g = 5 ± 0. 5 mm by the helicoid spring specimen technique at homologous temperatures ranging from 0.63 to 0.74 and applied stresses of 0.13 to 1.42MPa. At stresses lower than about 0.50 MPa, Bingham-type viscous creep with activation energy Q = 80 ± 25 kJ/mol, characterized by a threshold stress which decreases with increasing temperature, was predominant. At a stress above about 0.50 MPa, grain boundary sliding with a stress exponent n = 2 and Q = 85 ± 25 kJ/mol obviously contributed to the measured creep data. Stress redistribution was evaluated, and it did not greatly influence the stress exponent. The creep mechanisms were elucidated with respect to standard creep models supported by the substructures studied by transmission electron microscopy. Viscous creep (n = 1) was identical to be Harper-Dorn creep controlled by dislocation core diffusion. The motion of jogs on edge dislocations dependent on dislocation core diffusion was observed to control the creep. Grain boundary sliding accommodated by slip with n = 2 was noted, while hardening and the recovery of dislocations at grain boundaries were suggested to control the creep. Microstructural observations along with a determination of parametric variations in the creep rates were useful for identifying the underlying deformation mechanisms.

DOI： 10.2320/matertrans.M2011143

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructure in a high-density MgB2 wire fabricated by an internal Mg diffusion (IMD) process has been investigated by electron microscopy imaging and analysis at different scales. In the IMD process, a pure Mg rod was used as Mg source, and nanosized SiC powders were mixed with amorphous B powders. In the case of a heat treatment at 640 degrees C for 1 h carried out after rolling and drawing processes, the wire has two microstructural features that degrade critical current density: uncrystallized zones composed mainly of unreacted B and SiC powders, and cracks partly filled with course Mg2Si crystals. Those cracks were formed in the uncrystallized zones as well as in crystallized MgB2 zones. It indicate that the cracks formed by the mechanical milling and drawing remain after the heat treatment. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2011.05.143

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Creep of high-purity aluminum (5N Al) at room temperature and ultra-low strain rate was investigated by a high sensitive helicoid-spring specimen technique under conditions of constant and changing stress. Creep deformation consists of transient creep stages, and no secondary creep stage was observed. Li's equation showed a good fit to the experimental curves. During nominal steady-state creep, the stress exponent is equal to one regardless of initial state of specimens. However, the nominal steady-state creep rate for water quenched 5N Al is one order less than that for the static recovered specimens due to work hardening. With increase in stress, creep strengthening (the creep rate progressively decreasing in subsequent segments) was observed, which is due to different hardening remains because changing-stress creep experiment was conducted in the transient creep stage. Those phenomena of work hardening indicate creep deformation is controlled by recovery and work-hardening mechanism. During transient creep, every decrease in stress is associated with the large and long anelastic backflow. The anelastic transient strain for stress reduction is equivalent to elastic deformation corresponding to the applied stress, while transient strain is 2.5 times greater than the equivalent elastic deformation regardless of whether stress increases or is constant. The transient effect was suggested to be due to a mix of anelastic behavior caused by the internal redistribution of stress and inelastic behavior.

DOI： 10.2320/matertrans.M2011175

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructure in a high-density MgB₂ wire fabricated by an internal Mg diffusion (IMD) process has been investigated by electron microscopy imaging and analysis at different scales. In the IMD process, a pure Mg rod was used as Mg source, and nanosized SiC powders were mixed with amorphous B powders. In the case of a heat treatment at 640 °C for 1 h carried out after rolling and drawing processes, the wire has two microstructural features that degrade critical current density: uncrystallized zones composed mainly of unreacted B and SiC powders, and cracks partly filled with course Mg ₂Si crystals. Those cracks were formed in the uncrystallized zones as well as in crystallized MgB₂ zones. It indicate that the cracks formed by the mechanical milling and drawing remain after the heat treatment.

DOI： 10.1016/j.physc.2011.05.143

記述言語：英語  

In an in situ powder-in-tube (PIT) fabrication of MgB2 superconducting tapes, it has been found that ballmilling treatment on a starting powder is effective for improving critical current density (Jc) of the MgB₂ tapes. In the present study, microstructures/nanostructures of MgB2 tapes and the mechanism of the Jc enhancement by the ball milling treatment were investigated by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. A mixed powder of Mg and amorphous B was ball milled for 4 h. The milled powder was packed in a pure Fe tube and then cold rolled into a tape specimen. A heat treatment was performed at 600 C for 1 h under an Ar atmosphere and subsequently furnace cooled. MgB₂ tape specimens without the ball-milling treatment were also prepared for comparison. A focused ion beam (FIB)-microsampling technique was used for TEM specimen preparation. The MgB₂ tape with the ball-milling treatment exhibited a dense and uniform microstructure mainly composed of nano-crystalline MgB2. On the other hand, MgB₂ tapes without the ball-milling treatment showed inhomogeneous microstructures that comprise of a porous uncrystallized area and a crystallized one. It was also found that the averaged grain size of the nano-crystalline MgB₂ becomes smaller by the ball-milling treatment. Thus, it can be explained that the Jc enhancement by the ball-milling treatment is owing to improvements in the grain connectivity and microstructural uniformity of the crystalline MgB₂ phase in the tape.

DOI： 10.1063/1.4730732

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Predominantly two kinds of antiphase boundaries (APBs) form in Al5Ti3, which is an Al-rich ordered derivative of the -TiAl (L10) phase. This phase can be viewed as a periodic arrangement of lean rhombs and squares on the Ti-rich (002) planes of the tetragonal L10. Energies of the two types of APBs were varied in a Monte Carlo simulation by suitably changing the pair interaction parameters. APBs of both types form boundaries of Al5Ti3 antiphase domains (APDs), which coarsen with time. An important observation in this regard is that mostly facetted APBs form at lower ageing temperatures, whereas curved APBs appear to form at relatively higher ageing temperatures. The findings of this work suggest that there exists a critical temperature, akin to the roughening transition temperature for crystals, that marks the transition from facetted to curved APBs.

DOI： 10.1080/14786435.2011.563761

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90° ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils.

DOI： 10.1016/j.ultramic.2011.03.021

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Electron tomography requires a wide angular range of specimen-tilt for a reliable three-dimensional (3D) reconstruction. Although specimen holders are commercially available for tomography, they have several limitations, including tilting capability in only one or two axes at most, e.g. tilt-rotate. For amorphous specimens, the image contrast depends on mass and thickness only and the single-tilt holder is adequate for most tomographic image acquisitions. On the other hand, for crystalline materials where image contrast is strongly dependent on diffraction conditions, current commercially available tomography holders are inadequate, because they lack tilt capability in all three orthogonal axes needed to maintain a constant diffraction condition over the whole tilt range. We have developed a high-angle triple-axis (HATA) tomography specimen holder capable of high-angle tilting for the primary horizontal axis with tilting capability in the other (orthogonal) horizontal and vertical axes. This allows the user to trim the specimen tilt to obtain the desired diffraction condition over the whole tilt range of the tomography series. To demonstrate its capabilities, we have used this triple-axis tomography holder with a dual-axis tilt series (the specimen was rotated by 90 degrees ex-situ between series) to obtain tomographic reconstructions of dislocation arrangements in plastically deformed austenitic steel foils. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ultramic.2011.03.021

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε̇, lower than 10^-10 s^-1 and low temperature ranging from 0.32T_m to 0.43T _m. It was found that the creep behavior in this region depends strongly on grain sizes and impurity concentrations. For high-purity aluminum (5 N Al) with an average grain size, d_g > 1600 μm, nearly the wire diameter of the spring sample, where the role of grain boundary during creep deformation can be negligible, the stress exponent was n ∼ 5 and the activation energy was Q_c = 32 kJ/mol. Microstructural observation showed the formation of large dislocation cells (∼10μm) and tangled dislocations at the cell walls. For high-purity aluminum (5N Al) with d _g = 24 μm, the stress exponent was n ∼ 1 and the activation energy was Q_c = 15kJ/mol. On the other hand, for commercial low-purity aluminum (2 N Al) with d_g = 25 μm, the stress exponent was n = 2 and the activation energy was Q_c = 25 kJ/mol. Microstructural observations revealed dislocations emitted from grain boundaries, those dislocations interacting with intragranular dislocations and the formation of dislocation cells in the grains. Based on those experimental results, the low-temperature creep mechanisms in pure aluminum at ε̇ < 10^-10 s^-l have been discussed.

DOI： 10.2320/matertrans.M2010405

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Several reaction-induced diffusion processes to fabricate high-density MgB₂ materials are developed, and the critical current density (J_c) has been notably enhanced. In this study, microstructure in high-density MgB₂ wires fabricated by an internal Mg diffusion (IMD) process has been investigated. The inner reacted region of the wire heat-treated at 640 °C for 1 h shows dense polycrystalline MgB₂ of 20-200 nm in grain sizes. Fine MgO and Mg₂Si particles of 10-30 nm in sizes are dispersed in this region. On the other hand, the outer region near the Ta sheath is composed of unreacted B and SiC powders, fine MgO particles and small voids. Sizes of voids in the IMD MgB₂ wire are small compared with the PIT MgB₂ wire. Oxidation of Mg in the IMD process forms fine dispersion of MgO which may be effective for flux pinning.

DOI： 10.1109/TASC.2010.2091097

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bridge-shaped free-standing Si membranes (FSSM), strained by low-pressure (LP) Si_xN_y, plasma-enhanced (PE) Si_xN _y and Si_xGe_1-x stressors, were measured by convergent beam electron diffraction (CBED) and the finite element method (FEM). The results of CBED show that, while the strain along the length of the FSSM is compressive in an LPSi_xN_y/Si sample, those along the length of the FSSM are tensile in PESi_xN_y/Si and Si_xGe_1-x/Si samples. The average absolute values of strains are different in FSSM with LPSi_xN_y, PESi_xN_y and Si_xGe_1-x as stressors. The FEM was used to compensate the results of CBED taking into account the strain relaxation in transmission electron microscopy (TEM) sample preparation. The FEM results give the strain properties in three dimensions, and are in good agreement with the results of CBED. There is approximately no strain relaxation along the length of FSSM, and the elastic strains along the other two axes in FSSM are partially relaxed by thinning down for the preparation of TEM samples.

DOI： 10.1016/j.actamat.2011.01.031

記述言語：英語  

The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε, lower than 10^-10 s^-1 and room temperature, 298 K. It was found that the creep behavior at the very low ε depends strongly on grain sizes and impurity concentrations: in highpurity aluminum (5 N Al) with an average grain size of 24 μm, the stress exponent was n ~ 1; while, when the average grain size was larger than 1600 μm, the stress exponent was n ~ 5. Microstructural observation shows the formation of large dislocation cells, 10 μm. On the other hand, in commercial low-purity aluminum (2 N Al) with the average grain size of 25 μm, the stress exponent was n = 2. Microstructural observations revealed dislocations emitted from grain boundaries and the formation of lattice dislocation cells. To evaluate creep deformation mechanisms of the pure aluminum, stress change tests were conducted during creep tests. It was revealed that the deformation in the range of the stress exponent, n ~ 5, was controlled by recovery driven by internal stress, σ_i, because instantaneous strains at stress increment were larger than that at stress reduction. While the deformation behaviors in the ranges of the stress exponents, n ~ 1 and n = 2, were in viscous manner, because instantaneous strains at stress increment and reduction were in the same level. Based on those experimental results, the creep mechanisms have been discussed.

DOI： 10.1002/9781118062142.ch70

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The creep behavior in pure aluminum has been investigated by helicoid spring creep tests at strain rates, ε, lower than 10^-10 s ^-1 and room temperature, 298 K. It was found that the creep behavior at the very low ε depends strongly on grain sizes and impurity concentrations: in high-purity aluminum (5 N Al) with an average grain size of 24 μm, the stress exponent was n ∼ 1; while, when the average grain size was larger than 1600 μm, the stress exponent was n ∼ 5. Microstructural observation shows the formation of large dislocation cells, 10 μm. On the other hand, in commercial low-purity aluminum (2 N Al) with the average grain size of 25 μm, the stress exponent was n = 2. Microstructural observations revealed dislocations emitted from grain boundaries and the formation of lattice dislocation cells. To evaluate creep deformation mechanisms of the pure aluminum, stress change tests were conducted during creep tests. It was revealed that the deformation in the range of the stress exponent, n ∼ 5, was controlled by recovery driven by internal stress, ^σi, because instantaneous strains at stress increment were larger than that at stress reduction. While the deformation behaviors in the ranges of the stress exponents, n ∼ 1 and n = 2, were in viscous manner, because instantaneous strains at stress increment and reduction were in the same level. Based on those experimental results, the creep mechanisms have been discussed.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Dislocation density within ultrafine grains in severely deformed aluminium was evaluated by the scanning transmission electron microscopy. The values were around 10¹⁴m^-2 in commercial pure aluminium samples with equivalent strain up to 10. The obtained dislocation densities values correspond to strength between 55MPa and 70MPa according to the Bailey-Hirsch relationship.

DOI： 10.1016/j.msea.2010.09.058

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 n m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed.

DOI： 10.1080/14786435.2010.510453

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Effect of partial substitution of Mo in Ni3Mo by Mn on its ordering behaviour is studied here using Transmission Electron Microscopy (TEM). The change in alloy composition does not change the nature of the short range ordered (SRO) state, which shows intensity maxima at {1 1/2 0} and equivalent positions. However, prolonged aging at 973 K leads to transformation of the Ni₇₅Mo₁₅Mn₁₀ alloy, studied here, almost entirely into the ordered D0₂₂ phase unlike in the case of the binary Ni-Mo alloy. Curved antiphase boundaries (APBs), with wetting of the interdomain D0₂₂ regions by the disordered phase, characterize the microstructure of the aged alloy. A small volume fraction of a sigma-like topologically close packed (TCP) phase that appears in the as quenched alloy seems to remain unaffected by ageing.

DOI： 10.1007/s12666-010-0125-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Effect of partial substitution of Mo in Ni3Mo by Mn on its ordering behaviour is studied here using Transmission Electron Microscopy (TEM). The change in alloy composition does not change the nature of the short range ordered (SRO) state, which shows intensity maxima at {1 1/2 0} and equivalent positions. However, prolonged aging at 973 K leads to transformation of the Ni75Mo15Mn10 alloy, studied here, almost entirely into the ordered D0(22) phase unlike in the case of the binary Ni-Mo alloy. Curved antiphase boundaries (APBs), with wetting of the interdomain D0(22) regions by the disordered phase, characterize the microstructure of the aged alloy. A small volume fraction of a sigma-like topologically close packed (TCP) phase that appears in the as quenched alloy seems to remain unaffected by ageing.

DOI： 10.1007/s12666-010-0125-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Strain in a bridge-shaped freestanding Si membrane (FSSM) induced by depositing an amorphous Si_xN_y layer was measured by convergentbeam electron diffraction (CBED) and the finite element method (FEM). CBED results show that the strain magnitude depends negatively on the FSSM thickness, and compressive strain along the length of the FSSM is increased by approximately 0.1% at the end of the FSSM. FEM is used as a supplementary method to CBED for calculating the strain relaxation in three-dimension in the FSSM.

DOI： 10.1143/JJAP.49.090208

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Strain was induced in a bridge-shaped freestanding Si membrane (FSSM) by depositing an amorphous Si_xN_y layer to surround the Si membrane. Convergent beam electron diffraction revealed that compressive strain is distributed uniformly along the horizontal direction in Si_xN _y-deposited FSSM. On the other hand, strain decreases to almost zero at the ends of the FSSM, where the Si_xN_y layer beneath the Si layer is replaced by a SiO₂ buried oxide layer.

DOI： 10.1016/j.tsf.2010.06.023

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Strain in a bridge-shaped freestanding Si membrane (FSSM) induced by depositing an amorphous Si_xN_y layer was measured by convergent-beam electron diffraction (CBED). CBED results show that the strain magnitude depends negatively on the FSSM thickness. FEM is a supplement of the result of CBED due to the relaxation of TEM samples during fabricating. The FEM analysis results ascertain the strain property in three dimensions, and show that the strain magnitude depends negatively on the length of FSSM, and the magnitude of the compressive strain in FSSM increases as the position is closer to the upper Si/Si_xN_y interface.

DOI： 10.1016/j.msea.2010.07.004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The addition of Cr to (Mo_0.85Nb_0.15)Si₂ crystals significantly improves the thermal stability of the lamellar structure composed of C11_b-MoSi₂ and C40-NbSi₂ phases. Analysis using electron microscopy indicates the segregation of Cr atoms at the C40/C11_b lamellar interface. This leads to a decrease in the lattice misfit strain at the interface and better thermal stability of the lamellae.

DOI： 10.1016/j.scriptamat.2010.01.002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In order to clarify crack propagation behavior of alumina (α-Al₂O₃), intergranular and transgranular fractures of alumina were investigated by electron microscopy techniques. For the intergranular fractures cracked grain boundaries were investigated by scanning electron microscopic electron back-scattered diffraction (SEM-EBSD) analysis. It was revealed that the intergranular fracture behavior of polycrystalline alumina with random distribution of crystallographic orientations is independent on grain boundary characters. For the transgranular fractures, fracture surfaces formed in a single-crystalline alumina were observed by electron tomography combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and high resolution TEM (HR-TEM). Three kinds of fracture surfaces were observed: even fracture surfaces, even fracture surfaces with step-terraces and fracture surfaces composed of the even fracture surface and the curved one. The even fracture surfaces mostly consist of cleavage planes parallel to {1 over(1, ̄) 0 2} and {1 over(1, ̄) 0 4}. On the other hand, the even fracture surfaces with step-terraces consist of the cleavage planes and basal planes (0 0 0 1). For the fracture surfaces composed of the even fracture surface and the curved one, both the even and curved shapes the even parts were formed by the fine cleavage planes and basal planes, whose intervals were inhomogeneous. It was indicated that the fracture surfaces in alumina are composed of the cleavage planes or basal plane at an atomic scale.

DOI： 10.1016/j.ijfatigue.2009.06.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effects of plastic deformation on lamellar structure formation in solution-treated Ti-39 at.% Al single crystals were investigated, focusing on the role of dislocations of different slip systems. The dislocations were introduced by indentation on the surfaces of solution-treated single crystals with different crystallographic orientations. Traces of basal and prism slips were observed, depending on the position relative to the indentation. During annealing at α₂ + γ dual-phase temperatures, lamellar structures were formed faster where basal slip had occurred than where prism slip had occurred. After long annealing, the length scale of lamellar structures formed depends on the slip system operated during prior deformation: in the region where only one of either basal or prism slip had occurred the lamellar structure was coarser than in undeformed crystal, while in the region where both basal and prism slips occurred the lamellar structure was finer than those formed in undeformed crystal. The reasons for the differences in lamellar structures are discussed on the basis of the frequencies of stacking fault formation on (0 0 0 1) planes as precursors to γ-precipitates. The results suggest that the cross-slip of dislocations between basal and prism planes, which gives rise to the formation of multiple stacking faults on many parallel (0 0 0 1) planes, is responsible for the refinement of lamellar structures.

DOI： 10.1016/j.actamat.2009.10.027

記述言語：英語   掲載種別：研究論文（学術雑誌）  

This paper reports the mechanical property and crack propagation behavior of thin ceramics. A method to evaluate the stress intensity factor, K _I, of thin ceramics was proposed. Dependence of K_I values on the average grain size, d, of thin α-alumina were measured by the method. K_I values of thin α-alumina decreased with increasing d values from 4.3 μm to 15.2 μm, while the KI values were almost constant for 15.2 μm ≤d≤63.0 μm. The trend of K_I values agreed with the dependence of fracture toughness, K_c, of bulk α-alumina. The thin α-alumina specimens after crack propagation were investigated by scanning electron microscopic electron back-scattered diffraction (SEM/EBSD) analysis. Branched cracks were hardly observed, regardless of grain size. The result indicates that the toughing mechanism do not occur in the thin α-alumina. Dependence of the transgranular fracture rate, F, and the crack deflection rate, D, on d were measured from the orientation distribution maps. However, the F values and the D values were independent of d and approximately constant. The F values and D values depend on d in bulk α-alumina. It indicates that the crack propagation behavior is varied by thinning α-alumina.

DOI： 10.2320/jinstmet.74.24

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Crack tip dislocations and dislocations introduced by three point-bending tests at high temperature are observed by combinating scanning transmission electron microscopy and computed tomography (STEM-CT). Commercially available P type (001) single crystal silicon wafers were employed. A series of STEM image was acquired from -60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. Reconstructed images of dislocations revealed dislocation structures in three-dimension.

DOI： 10.4028/www.scientific.net/AMR.89-91.473

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Three-dimensional Visualization of Dislocations Using Two Diffraction Conditions

DOI： 10.2320/materia.48.610

記述言語：日本語  

We report relationships between the superconducting properties, microstructure and fabrication conditions in high-density MgB₂ bulks fabricated using a premix-powder-in-closed-tube (PICT) method. The microstructure of the MgB₂ bulks depends on the crystallinity of the initial B powders; use of crystalline B powders reduces the amount of MgB₂ and increases re-sidual B and MgO. The heat treatment condition influences the grain sizes of MgB₂ as well as the distribution and grain sizes of MgO. A lower temperature and a shorter duration of heat treatment tend to form fine grains of MgB₂ and uniform dispersion of fine MgO particles. These microstructural variations influence the distribution of effective flux pinning centers such as grain boundaries and fine MgO particles. Different types of critical current density behavior as a function of magnetic field were meas-ured.

DOI： 10.2221/jcsj.44.613

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We were successful for three-dimensional imaging of microstructures in YBa₂Cu₃O_7-y (Y123) films fabricated by metal organic deposition using trifluoroacetates (TFA-MOD) method. We have reported previously, that a transmission electron microscopy (TEM) analysis clarified microstructures such as Y123 crystal grains and pores in the Y123 films. In order to derive important parameters for enhancement of superconducting properties of the Y123 films, quantitative analyses of those microstructures are required. Then, control of both pores and a-axis oriented grains distribution in the Y123 films are important. However, general TEM images provide only a two-dimensional projection of a three-dimensional object. An electron tomography is an effective technique for three-dimensional structure analysis of various materials. Cross-sectional view specimen for the three-dimensional electron tomography was prepared by focused ion-beam milling equipped with micro-sampling system. A scanning transmission electron microscopy - annular dark field technique was used for the present three-dimensional electron tomography. For the cross-sectional specimen of fired Y123 films, three-dimensional shapes and distributions of both pores and unreacted phases were observed in reconstructed images. Also, morphologies of the Y123 film surface were clearly seen.

DOI： 10.1016/j.physc.2009.05.059

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We prepared the multilayered MgB₂ /Ni thin films with the Ni layer spacings of 32, 23 and 16 nm. The MgB₂/Ni multilayer nanostructure was confirmed to be obtained from the scanning transmission electron microscope observation. The clear enhancement of J_c was observed in the multilayered MgB₂/Ni thin film when the magnetic field was applied parallel to the film surface. Moreover, the peak position of F_P - B curves shifted to higher magnetic field with decreasing the Ni layer spacing.

DOI： 10.1109/TASC.2009.2018527

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In the field of electronics, it is crucial to guarantee long-term joint reliability of the Sn-Ag-Cu solder alloy. Creep tests in low-stresses are necessary to guarantee the reliability. However, a very long period of time is required for the creep tests. To decide a steady-state creep strain rate, an approximate equation of a creep curve was newly applied to the helical spring creep test known as a method of a low-stress creep test. Obtained results are as follows. (1) The torsional strain component is decreased with the deformation of the helical spring shaped specimen. Therefore, the steady-state creep rate cannot be detected in the helical spring creep test. The approximate equation of a creep curve introduced by Li's group was found to be effective to obtain the steady-state creep rate for Sn-based solder alloy. (2) The helical spring creep testing method that uses the torsional deformation of the test specimen is more effective for the Sn-based solder alloy with a strong anisotropy of strength than the uniaxis creep testing method. (3) In the heat-treated Sn-3.0 mass%Ag-0.5 mass%Cu solder alloy, the creep stress exponent changed from 19 into 1.1 on the boundary of about 14 MPa. This result implies that the creep deformation mechanism was changed from the dislocation creep with dispersion-strengthening to the grain boundary sliding. This phenomenon was found for the first time by using the helical spring creep testing method.

DOI： 10.2320/jinstmet.73.373

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The stress-induced martensitic phase transformation from a tetragonal (t) phase to a monoclinic (m) phase in a CeO₂ doped tetragonal polycrystal (Ce-TZP) was investigated from the view pints of characters of lattice correspondences (LCs) between tand m-phases and morphology of m-phase. Electron back scattering diffraction (EBSD) analysis in the vicinity of Vickers indentations in Ce-TZP reveled that there were three LCs, named LCA (type A), LCB (type B) and LCC (type C), where fractions of the three LCs were 12%, 8% and 80%, respectively. Morphology of m-phase showing each of the three LCs were observed by transmission electron microscopy (TEM). A single variant of mphase with lamellar plate-shaped morphology (m-plates) was formed near the Vickers indentations. In contrast, two variants of m-phases with twin relationships (m-twins) were formed far from the Vickers indentations. The infinitesimal-deformation theory was adopted to calculate scalar magnitude of internal stress within the m-plates and m-twins for each type of the LCs. Irrespective of morphology of the m-phase, the internal stress field for type C is a tensile stress field. Regardless of the type of LCs, absolute values of internal stress in the m-plates are higher than those in the mtwins.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2320/matertrans.E2008002

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Three-Dimensional Imaging of Crystalline Microstructures Using Electron Tomography

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Crack tip dislocations in silicon single crystals have been observed by a combination of annular dark-field scanning transmission electron microscopy and computed tomography. A series of images was acquired by maintaining the diffraction vector parallel to that of crack propagation to achieve sharp images of the dislocations. The observed dislocations were reconstructed by a filtered back-projection, and exhibited three-dimensional configurations of overlaid dislocations around the crack tip.

DOI： 10.1016/j.scriptamat.2008.06.042

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Crack tip dislocations in silicon single crystals have been observed by a combination of annular dark-field scanning transmission electron microscopy and computed tomography. A series of images was acquired by maintaining the diffraction vector parallel to that of crack propagation to achieve sharp images of the dislocations. The observed dislocations were reconstructed by a filtered back-projection, and exhibited three-dimensional configurations of overlaid dislocations around the crack tip. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.scriptamat.2008.06.042

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from -60° to +60° in tilt range with 2° in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending.

DOI： 10.2320/matertrans.MAW200828

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Dislocations in a silicon single crystal introduced by three point-bending at a high temperature were observed by electron tomography in annular dark field-scanning transmission electron microscopy (ADF-STEM). Commercially available P type (001) single crystal wafers were employed. An ADF STEM tilt series was acquired from -60 degrees to +60 degrees in tilt range with 2 degrees in tilt step. The diffraction vector was maintained close to g(hkl) = 220 during the acquisition by adjusting the [110] direction of the sample parallel to the tilt axis of the holder. The observed dislocations were reconstructed by simultaneous interactive reconstruction technique, exhibiting a 3-D configuration of dislocations introduced by the three-point bending. [doi: 10.2320/matertrans.MAW200828]

DOI： 10.2320/matertrans.MAW200828

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Electrical and Stractural Evaluations of Ultrathin SiGe-and Ge-on-insulator Fabricated Using Ge Condensation by Dry Oxidation

DOI： 10.7567/ssdm.2008.p-3-18

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The ordering mechanism of long-period superstructures (LPSs) in Al-rich TiAl alloys has been investigated by high-resolution transmission electron microscopy (HRTEM). The LPSs are classified in terms of arrangements of base clusters with different shapes and compositions formed in Ti-rich (002) layers of L 1₀-TiAl matrix: square Ti₄Al, fat rhombus Ti₃Al, and lean rhombus Ti₂Al type clusters. The HRTEM observations revealed that antiphase boundaries of long-range-ordered LPS domains and short-range-ordered microdomains are constructed by various space-filling arrangements of the base clusters. Such a microscopic property characterized by the base clusters and their arrangements is markedly analogous to that of the 〈1,1/2,0〉* special-point ordering alloys such as Ni-Mo.

DOI： 10.1007/s11661-007-9397-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The ordering mechanism of long-period superstructures (LPSs) in Al-rich TiAl alloys has been investigated by high-resolution transmission electron microscopy (HRTEM). The LPSs are classified in terms of arrangements of base clusters with different shapes and compositions formed in Ti-rich (002) layers of L1(0)-TiAl matrix: square Ti(4)Al, fat rhombus Ti(3)Al, and lean rhombus Ti(2)Al type clusters. The HRTEM observations revealed that antiphase boundaries of long-range-ordered LPS domains and short-range-ordered microdomains are constructed by various space-filling arrangements of the base clusters. Such a microscopic property characterized by the base clusters and their arrangements is markedly analogous to that of the < 1,1/2,0 >* special-point ordering alloys such as Ni-Mo.

DOI： 10.1007/s11661-007-9397-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A study was conducted to perform 3D microstructural analysis based on electron tomography. The study also attempted to investigate a unique domain structure in a Ni-Al-Ti alloy. A two-phase microstructure,composed of L1 ₂-ordered γ domains with cuboidal shape and an A1-disordered γ matrix exhibited secondary phase separation during aging precipitation of fine γ in each domain. A variety of precipitation behaviors and microstructural evolutions were observed in the second stage of phase separation, depending on on the alloy composition. The study also demonstrated tomographic DFTEM and EFTEM observations, to clarify the 3D morphology of the γ precipitates and compositional distribution in the phase-separated microstructure.

DOI： 10.1002/adma.200702461

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Advanced electron tomography enables the visualization of 3D domain structures in crystalline materials (see figure) In this study, the morphology and composition of gamma'(L1(2)-ordered) and gamma (Al-disordered) domains formed in Ni-based Ni-Al-Ti superalloys are investigated by tomographic dark-field and energy-filtered transmission electron microscopy.

DOI： 10.1002/adma.200702461

記述言語：英語   掲載種別：研究論文（学術雑誌）  

It has been reported that doping with aromatic hydrocarbons in an in situ powder-intube fabrication process of MgB₂ tapes is effective for increasing the critical current density (J_c) under magnetic fields. In this study, the mechanism of the J_c enhancement by doping with C₄H₄S was investigated by transmission electron microscopy (TEM). The C₄H₄S-doped MgB₂ tape has a denser cross-sectional microstructure than that of a non-doped MgB₂ tape. Electron diffraction and dark-field TEM observation indicated that the grains of MgB₂ are well crystallized and slightly increase in size with the C₄H₄S doping. X-ray diffraction and twodimensional elemental mapping using characteristic x-rays suggested that C atoms substitute part of B atoms in MgB₂ crystals. Unlike other kinds of impurity doping, such as SiC-doping, there were few nanosized inclusions formed by C ₄H₄S doping. Thus, it is concluded that the Jc enhancement with the C₄H₄S doping is due to (i) increasing supercurrent and magnetic-flux pinning at grain boundaries by the formation of dense and well-crystallized MgB₂ matrix and (ii) increasing the upper critical field by the formation of Mg(B,C)₂.

DOI： 10.1088/1742-6596/97/1/012277

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Macroscopic features of crack propagation behavior in polycrystalline alumina (poly-alumina) and alumina single crystals (single-alumina) were analyzed by scanning electron microscopic electron back-scattered diffraction (SEM-EBSD) analysis. It was revealed that the intergranular fracture behavior is independent on grain boundary characters. When the cracks are propagated in the grains of poly- or single-alumina, zigzag cracks were produced. The zigzag cracks are composed of fracture surfaces formed along the cleavage planes. Microscopic features of fracture surfaces formed in a single-alumina were observed in detail by electron tomography combined with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). It was by visualized that the zigzag cracks were composed of flat and uneven fracture surfaces at a nm scale. The flat fracture surfaces and uneven ones were nearly parallel to the cleavage plane, {11̄02}, and the basal plane, {0001}, respectively.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bottom-channel hole mobility was examined by a pseudo-metal-oxide- semiconductor field-effect transistors method for ultrathin SiGe-on-insulator (SGOI) and Ge-on-insulator (GOI), which were fabricated using Ge condensation by dry oxidation. By comparing samples with and without a top SiO2 layer, we investigated the influence of top surface passivation on bottom-channel hole mobility. Mobility degradation was found in an ultrathin SGOI/GOI layer without top SiO2 and became more serious with a decrease in the thickness of the SGOI/GOI layer, which strongly suggested that top surface passivation is necessary to evaluate accurate channel mobility. A 13-nm-thick GOI with passivation showed a high mobility value of 440 cm2 /V s.

DOI： 10.1063/1.2972114

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

The interaction of amorphous silicon (a-Si) and aluminum (Al) has been examined using in-situ transmission electron microscopy. Carbon coated nickel grids were used for depositing thin (∼50nm) amorphous silicon films using ultra high vacuum cluster tool and a thin film of Aluminum (∼50nm) was deposited subsequently on a-Si film by sputtering. The grid containing a-Si and Al films was mounted on a heating holder of FEI 200kV TEM and loaded in the TEM for viewing the microstructural and phase transformations during the in-situ heating process. The microstructural features and electron diffraction patterns in the plain view mode were observed with increase in temperature starting from 30 °C to 275 °C. The temperatures used in this experiment were 30,100,150,200, 225, 275°C . A sequential change in microstructural features and electron diffraction pattern due to interfacial diffusion of boundary between Al and amorphous Si was investigated. Evolution of polycrystalline silicon with randomly oriented grains as a result of a-Si and Al interaction was revealed. After the in-situ heating experiment the specimen was taken out and etched to remove excess of Al and the subjected to high resolution imaging under TEM and EDS analysis. The EDS analysis of the crystallized specimen was performed to locate the Al distribution in the crystallized silicon. It has been shown that Al induced crystallization can be used to convert sputtered a-Si into polycrystalline silicon as well as nanocrystalline silicon at a temperature near 275 °C by controlling the in-situ annealing parameters. The mechanism of AIC has been discussed from the experimental results and the phase diagram of Al-Si system.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We prepared MgB₂/Ni and MgB₂/B alternately-layered films using electron beam evaporation and coaxial vacuum arc evaporation techniques without any post-annealing. The thickness of each MgB₂ layer was designed to be 42, 24 or 15nm for both MgB₂/Ni and MgB ₂/B alternately-layered films. We confirmed that the layered structure was successfully obtained from the scanning transmission electron microscopic cross-sectional image of the MgB₂/Ni alternately-layered film. The critical temperature, T_c, of the alternately-layered film decreased as the MgB₂ layer became thinner, for both MgB ₂/Ni and MgB₂/B films. Moreover, the T_c was affected by only the MgB₂ layer thickness, and was independent of the inserted layer materials.

DOI： 10.1088/0953-2048/20/12/023

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

3D Observation of Dislocations in Si Single Crystal using a High-angle Triple-axis (HATA) Specimen Holder

DOI： 10.2320/materia.46.785

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Transmission electron microscope (TEM) analysis was performed for the anti-surfactant (AS)-treated interface of GaN thin films deposited by the metal-organic vapor-phase epitaxy method. It was revealed that the AS-treatment with supplying a gas-source of tetraethyl-silicon (TESi) forms an interface layer of about 1 nm thickness. The electron diffraction pattern for the interface layer shows a streak along [0 0 0 1] at about one-thrid positions between hkil=0 0 0 0 and over(1, -) 2 over(1, -) 0. The point analysis of energy dispersive X-ray spectroscopy (EDS) confirmed that the interface layer contains a certain amount of silicon. These results revealed that the interface layer is a crystalline phase of silicon compound. The effect of the interface layer on the morphology of threading dislocations was also discussed in terms of coherency of the interface layer with GaN.

DOI： 10.1016/j.jcrysgro.2006.10.188

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures of MgB₂/Fe tapes fabricated by an in situ powder-in-tube method using MgH₂ as a precursor powder have been studied by means of x-ray diffraction and analytical transmission electron microscopy combined with a focused ion beam microsampling technique. The overall microstructures in the tapes are characterized as densely crystallized MgB₂ areas with 10-200 nm grain size, uncrystallized areas mainly containing MgO and amorphous phases enriched with B, and a number of holes and cracks. The crystallized MgB₂ areas increase upon doping with SiC nanoparticles. Si and C atoms decomposed from SiC nanoparticles during heat treatment exhibit different spatial distributions: the Si atoms are inhomogeneously distributed, forming silicides such as Mg₂Si with grain size of 5-20 nm, while the C atoms tend to be uniformly distributed in the MgB₂ matrix. A significant difference in distribution of O atoms between the SiC-doped and non-doped specimens was observed. The processes of formation of these microstructures and their relationships with the critical current density under magnetic fields have been discussed.

DOI： 10.1088/0953-2048/19/2/002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures of MgB2/Fe tapes fabricated by an it? situ powder-in-tube method using MgH2 as a precursor powder have been studied by means of x-ray diffraction and analytical transmission electron microscopy combined with a focused ion beam microsampling technique. The overall microstructures in the tapes are characterized as densely crystallized MgB2 areas with 10-200 nm grain size, uncrystallized areas mainly containing MgO and amorphous phases enriched with B, and a number of holes and cracks. The crystallized MgB2 areas increase upon doping with SiC nanoparticles. Si and C atoms decomposed from SiC nanoparticles during heat treatment exhibit different spatial distributions: the Si atoms are inhomogeneously distributed, forming silicides such as Mg2Si with grain size of 5-20 nm, while the C atoms tend to be uniformly distributed in the MgB2 matrix. A significant difference in distribution of O atoms between the SiC-doped and non-doped specimens was observed. The processes of formation of these microstructures and their relationships with the critical current density under magnetic fields have been discussed.

DOI： 10.1088/0953-2048/19/2/002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A plasma cleaner is usually used for removing carbonaceous debris from a specimen and preventing contamination during transmission electron microscopy (TEM) imaging and analysis. However, the plasma cleaner can be effectively used for thinning down damage layers on TEM specimens prepared by focused ion-beam (FIB) milling. By optimizing plasma treatment conditions, the quality of high-resolution images and diffraction patterns of the FIB-milled specimens has been remarkably improved using the plasma cleaner.

DOI： 10.1093/jmicro/dfl001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A plasma cleaner is usually used for removing carbonaceous debris from a specimen and preventing contamination during transmission electron microscopy (TEM) imaging and analysis. However, the plasma cleaner can be effectively used for thinning down damage layers on TEM specimens prepared by focused ion-beam (FIB) milling. By optimizing plasma treatment conditions, the quality of high-resolution images and diffraction patterns of the FIB-milled specimens has been remarkably improved using the plasma cleaner.

DOI： 10.1093/jmicro/dfl001

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Microstructural characterization was performed by analytical transmission electron microscopy (ATEM) to clarify the formation mechanism of tin whiskers. A tin (Sn)-layer about 10 μm thickness was electrodeposited on a FeNi42 plate. The Sn/FeNi42 plate was heated and cooled repeatedly in a temperature range of 233-403 K for 100 cycles under various atmospheres. Cross-sectional TEM specimens of whiskers on the Sn/FeNi42 plate were prepared using a focused ion beam (FIB) micro-sampling technique. Some artifact-effects of the FIB treatments on microstructures in tin alloys were taken into account. Bent-type whiskers grown on the Sn/FeNi42 are of polycrystalline β-Sn. A tin-oxide layer around 10 nm in thickness is formed on the tin surface. Electron diffraction, high-resolution TEM and electron energy loss spectroscopy (EELS) analyses revealed that the tin-oxide layer is predominantly of crystalline SnO 2. The presence of crystalline SnO was also recognized. It was found that the tin-oxide layer tends to be rather thin around stems of the whiskers. It is interpreted that thermal stress in the tin-layer breaks the thin tin-oxide layer at grain boundaries of tin and the whiskers grow from the broken area. The formation mechanism of the whiskers is discussed.

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Tin whiskers grown on a Sn/Cu-plated Polyimide (PI)-flexible substrate are a serious problem in electronic industrial application, because the whiskers lead to catastrophic electrical short circuit failures. Here, we report characterization of microstructures in the whiskers grown on a surface of Sn/Cu-plated PI-flexible substrate by cross-sectional transmission electron microscopy (TEM) to analyze the behavior and the formation mechanism of whiskers. The whisker was found to be monocrystalline β-Sn and grown with the preferred directions of [110] and [101]. The whiskers formed on this tin surface are nucleated and grown by the compressive stress, that is induced externally by insertion of Sn/Cu-plated PI-flexible substrate into the connector.

DOI： 10.1109/EPTC.2006.342749

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A transmission electron microscopy (TEM) study has been carried out on an MgB₂/α-Al₂O₃ film that exhibits the typical property of critical current density (J_c) under magnetic fields. The MgB₂ layer of 300 nm in thickness was grown on a (001)α-Al₂O₃ substrate using an in situ electron beam evaporation method. J_c of the film takes significantly high values when the applied magnetic field is perpendicular to the film surface. The MgB₂ layer consists of fine columnar MgB₂ crystals 20-30 nm in size. The columnar MgB₂ crystals grow almost perpendicular to the substrate surface and have no crystallographic orientation relationship with the α-Al₂O₃ substrate because of an amorphous layer formed first on the substrate. A high density of columnar grain boundaries within the MgB₂ layer may be effective for the enhancement of the flux-pinning under the perpendicular magnetic field.

DOI： 10.1088/0953-2048/18/10/005

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The redox efficiency of iron has been improved by increasing the distribution of iron on the carbon surface with Fe₂O ₃-loaded carbon materials. The Fe₂O₃-loaded carbon material was prepared by loading Fe₂O₃ on carbon by a chemical method. Fe(NO₃)₃ was impregnated on carbon with different weight ratios of iron-to-carbon in an aqueous solution, and the mixture was dried and then calcined for 1 h at 400 °C in flowing Ar. The effect of various carbons on the physical and electrochemical properties of Fe₂O₃-loaded carbon electrodes was investigated with the use of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with X-ray energy-dispersive spectroscopy (EDS), cyclic voltammetry (CV) and galvanostatic cycling performance. Transmission electron microscopy coupled with X-ray diffraction measurements revealed that small Fe₂O₃ particles were distributed on the carbon surface. Natural graphite and several nano-carbon materials such as acetylene black and tubular carbon nanofibers (tubular CNF) exhibited improved characteristics, such as enhanced capacity and higher redox currents for the Fe₂O₃-loaded carbon electrode. SEM and EDS results suggest that Fe₂O₃-loaded nano-carbon electrodes, due to the large surface area of the nano-carbon, have more Fe₂O₃ dispersed than on Fe₂O₃-coated graphite electrodes.

DOI： 10.1016/j.jpowsour.2005.02.028

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Here we show a technique to obtain a tilt series of dark-field (DF) transmission electron microscopy (TEM) images in ordering alloys for tomographic three-dimensional (3D) observations. A tilt series of DF TEM images of D1(a)-ordered Ni₄Mo precipitates in a Ni-Mo alloy was successfully obtained by adjusting a diffraction condition for a superlattice reflection from the Ni₄Mo precipitates. Since the superlattice reflection usually has a long extinction distance, dynamic diffraction effects such as thickness fringes can be suppressed to some extent with precise realignment of the diffraction condition. By using the tilt series of the DF TEM images, we attempted a computed TEM tomography to visualize 3D shapes and positions of the precipitates.

DOI： 10.1093/jmicro/dfi060

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Annealing processes in MgB₂ films deposited on yttria-stabilized zirconia (YSZ)-buffered Hastelloy substrates were studied by transmission electron microscopy. The MgB₂ films with Mg-rich compositions were fabricated at room temperature using a pulsed laser deposition (PLD) method. The as-deposited films do not exhibit clear superconducting transitions, and have inhomogeneous microstructures composed of amorphous regions and a small amount of crystalline MgB₂ and MgO with several tens of nm in size. Various sizes of voids are also incorporated within the amorphous regions. After the annealing at 600 or 680°C, the films exhibit clear superconducting transitions. The amorphous regions crystallize into fine grains of MgB ₂ or MgO 5-50 nm in size. The voids remain in the annealed films and their sizes depend on the annealing condition. Magnesium-and oxygen-rich layers are formed near the MgB₂/YSZ interface and the film surface. It is suggested that the finer grains of MgB₂ and MgO obtained by the lower-temperature annealing give a larger critical current density under a high magnetic field.

DOI： 10.1109/TASC.2005.848834

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Magnesium diboride, MgB₂, thin films are fabricated through two different kinds of process. One is an in-situ process by using electron beam deposition and the other is an ex-situ process by using the combination of pulsed laser deposition and heat treatment. The critical current density, J _c, is investigated as a function of external magnetic field in the range of 0-7 T and/or temperatures ranging from 4.2 K to the critical temperature by using dc 4-probe transport method. The in-situ processed film shows very high J_c, e.g., 7.1×10⁶, 1.2×10 ⁶, and 1.4×10⁵ A/cm² in 0, 4, and 7 T (perpendicular fields), respectively. Angular dependence of J^c is much different between the two kinds of films. J_c-angle (magnetic field) curves of the in-situ processed film show two peaks; one is around the field perpendicular to the film surface and the other is around the parallel field. On the contrary, the curves of the ex-situ processed film have only one peak around the parallel field. Microstructure analyses show that the in-situ film has columnar grains aligned perpendicular to the film surface and that the ex-situ one has granular grains with random orientations. These results indicate that the grain boundaries between columnar grains act as effective pinning centers and enhance J_c in the perpendicular fields.

DOI： 10.1109/TASC.2005.848866

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A graded glass coating for Vitallium®, a Co-Cr alloy, has been prepared using a simple enameling technique. The composition of the glasses has been tailored to match the thermal expansion of the alloys. The optimum glass composition and firing conditions (temperature and time) needed to fabricate homogeneous coatings with good adhesion to the alloy were determined. The final coating thickness ranged between 25 and 60 μm. Coatings fired under optimum conditions do not delaminate during indentation tests of adhesion. Excellent adhesion to the alloy has been achieved through the formation of 100 nm thick interfacial chromium-oxide (CrOx) layers. The graded glass (consisting of BIG and 6P50 layers) can be successfully coated to a Co-Cr alloy, and forms hydroxyapatite (HA) on the coating surface when immersed in a simulated body fluid (SBF) for 30 days.

DOI： 10.1007/s10853-005-1982-z

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A series of long-period superstructures (LPSs) formed in an Al-rich TiAl single crystal with a gradient composition has been observed by transmission electron microscopy. A Ti-54.7?at.%?Al single crystal was heat treated within molten Al at 1234°C, and a composition-gradient layer with an Al concentration from 55 to 75?at.% was formed at the surface of the single crystal. The composition-gradient layer exhibits ordering into different LPSs depending on the Al concentration as follows: short-range order, h-Al2Ti and one-dimensional antiphase domain structure. These LPSs have an alternate stacking of Al(002) and Ti-Al(002) layers and the ordering of the LPSs proceeds in the TiAl matrix, maintaining an orientation relationship in which Al(002) layers of the LPSs and the TiAl matrix are parallel to each other. The ordering of this type of LPS and the phase transition between these LPSs are thus interpreted as structural changes in Ti(002) layers of the Al-rich TiAl crystal. It was also observed that ordering of the orthorhombic h-Al2Ti exhibits anisotropic features depending on the direction of the composition gradient. This suggests that the long-period ordering in the TiAl crystal depends on diffusion processes as well as the local concentrations of Ti and Al atoms.

DOI： 10.1080/09500830500157462

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The atomistic structure of a high-strength Cu42.5Ti41.5Ni7.5Zr2.5Hf5Si1 bulk metallic glass prepared by copper-mould casting has been characterized by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). High-resolution TEM and high-angle annular dark-field observations revealed that crystalline nanoparticles with sizes less than 10?nm are embedded in an amorphous matrix. It was confirmed by energy-dispersive X-ray spectroscopy in combination with STEM that these nanoparticles possess higher copper content than the amorphous matrix. Nanobeam electron diffraction experiments indicated that their crystalline structure is basically face-centred cubic with ordered atomic arrangements.

DOI： 10.1080/09500830500153776

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1017/S1431927605050026

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

For three-dimensional (3D) observation of microstructures in ordering alloys, such as orientation variants and anti-phase domain boundaries, electron tomography using dark-field transmission electron microscopy (DF TEM) may be a potential approach. However, DF TEM tomography has been thought to be impossible because of dynamical diffraction effects in crystals. In this study, we attempted DF TEM tomography of ordered and disordered precipitates in Ni-Mo and Ni-Al-Ti alloys. A tilt series of DF images of the precipitates were obtained by precisely setting diffraction conditions for a superlattice reflection. Owing to a long extinction distance of the superlattice reflection, dynamical diffraction effects, such as thickness fringes, have been effectively suppressed. Preliminary 3D reconstruction from the obtained tilt series clearly shows qualitative morphology and relative positions of the precipitates, which suggests the feasibility of the DF TEM tomography for ordering alloys.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The ordering mechanism of long-period superstructures (LPSs) in Al-rich Ti-Al alloys was studied using a TiAl single crystal with a composition gradient. A TiAl single crystal with gradient compositions from 55 to 75 at.% Al was prepared by annealing in a molten Al at 1234°C. The single crystal exhibits long-period ordering into different LPSs depending on the Al concentration as follows: an Al₅Ti₃ type short-range order, h-Al₂Ti and one-dimensional antiphase domain structures. These LPSs show an orientation relationship in which Al (002) layers of the LPSs are parallel to those of the TiAl matrix. The atomic arrangements of the LPSs are characterized in common as the alternate stacking of the Al (002) layers and Ti-Al (002) layers. It is thus concluded that the ordering of this type of LPSs and the phase transition between these LPSs are explained as structural changes in Ti-Al (002) layers of the Al-rich L1₀-TiAl crystal.

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Ordering process and subsequent formation of anti-phase boundaries (APBs) in the long-period superstructures of X₃Ti₂ (Ga ₃Ti₂), X₅Ti₃ (Al₅Ti ₃) and h-X₂Ti (h-Al₂Ti) in -rich TiX (X=Al or Ga) single crystals were examined by a high-resolution transmission electron microscopy. Formation of the APBs is closely related to the unique units of ordered base clusters such as Ti₄X, Ti₃X and Ti ₂X which form square, fat rhombus and lean rhombus shapes, respectively, in the (002) Ti-rich layers of the L1₀ matrix. The Al₅Ti₃-type anti-phase domains (APDs) with various sizes in diameter are introduced in Ti-62.5at.%Al crystals by appropriate heat treatment. Almost all the X₅Ti₃-type APBs lie on {110) and a type of APB (named Type A) with the extremely low APB energy was found. In contrast, no APBs are introduced in X₃Ti₂ and h-X ₂Ti because of their relatively higher energies compared with those in X₅Ti₃. As a result, the L1₀ matrix phase remains between APDs as a thin boundary phase for h-Al₂Ti.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Metastable long-period superstructures in an LI₀-TiAl single crystal with a composition gradient were observed successfully by transmission electron microscopy with a focused ion beam (FIB) microsampling technique. The composition gradient from 54.7 to 75 at.% Al with ∼6 μm width was detected by electron probe microanalysis and foil specimens containing the composition-gradient area were fabricated by the FIB microsampling method. The foil specimens clearly exhibit sequential changes in long-period superstructure depending on the Al concentration.

DOI： 10.1093/jmicro/dfh049

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In order to understand the relationship between the microstructures and superconducting properties of MgB₂ films, analytical TEM observations have been carried out. The films were fabricated by a KrF excimer laser deposition on Hastelloy substrates precoated with YSZ (yttria-stabilized zirconia). The deposited films were annealed under Ar atmosphere at 873 K for 1 h and at 953 K for 0.5 h. The critical current densities of these films were measured to be J_c=1×10⁵ A/cm² and J _c=7.7×10³ A/cm² at 4.2 K and 10 T, respectively. The conventional TEM observation showed nanocrystalline MgB ₂ and MgO of 5-30 nm in size dispersed in the films. Voids with various sizes from 10 to 60 nm were also observed in the films. Two-dimensional elemental analyses exhibited that near the MgB₂/YSZ interface the films have a layered structure where the layers enriched with Mg and O have low B concentrations complementarily. The average sizes of the MgB₂ and MgO grains and the voids increase with the annealing temperature. The enhancement of J_c value of the film annealed at 873 K may be due to smaller sizes of the MgB₂ and MgO grains and voids than those at 953 K.

DOI： 10.1016/j.physc.2004.01.168

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The production of critical current density (J_c) by 20-30 nm diameter columnar grains of MgB₂ was analyzed. It was observed that 20-30 nm diameter columnar grain structure produced J_c exceeding 5×10⁶ A/cm². It was also observed that strongest pinning ocurred when the field was aligned parallel to the grain boundaries. The results show that grain boundaries in MgB₂ do not obstruct current flow as in the high-temperature cuprate superconductors, but act like those in intermetallic superconductors such as Nb₃Sn.

DOI： 10.1063/1.1805195

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures of MgB ₂ films on yttria-stabilized-zirconia (YSZ) /Hastelloy substrates were studied by analytical transmission electron microscopy. The MgB ₂ films with Mg-rich compositions were fabricated by pulsed laser deposition followed by annealing at 600°C or 680°C under Ar atmosphere. Fine grains of MgB ₂ and MgO crystals 5-30 nm in size that shows a good mutual connectivity are formed in the MgB ₂ films. The MgB ₂ films also form voids 5-100 nm in size that may contain amorphous or oxide phases. Two-dimensional elemental analyses revealed that Mg and O atoms are enriched near the MgB ₂/YSZ interface. From a comparison in microstructures between the 600°C- and 680°C-annealed MgB ₂ films, it is suggested that the films composed of finer grains of MgB ₂ exhibit a higher critical current density under high magnetic fields.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Long-period superstructures formed in off-stoichiometric L1 ₀-TiAl alloys were investigated by high-resolution transmission electron microscopy (HRTEM). The HRTEM analysis combined with multislice simulation and image processing was carried out to clarify atomistic microstructures of Al₅Ti₃ and h-Al₂Ti ordered states and a short-range ordered (SRO) state in Ti-62.5 at.% Al alloys. Aluminium atoms in the (002) Ti layers form square-, lean rhombus- and fat rhombus-type ordered clusters in the SRO state. The ordered clusters are in contact with each other and form microdomains of various long-period superstructures. The ordered clusters are tiled periodically in a long range to form Al₅Ti₃ or h-Al₂Ti domains and characteristic antiphase boundary structures.

DOI： 10.1093/jmicro/53.1.1

記述言語：英語  

Formation of long-period superstructures in TiAl single crystal with composition-gradient

記述言語：英語  

Anti-phase boundary structure in Al5Ti3 long-period ordered TiAl alloys

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atomistic microstructures of long-period superstructures in Al-rich TiAl alloys were investigated by high-resolution transmission electron microscopy, The multi-slice image simulation revealed that Al-atoms in Ti-rich (002) layers of the superstructures are imaged as very bright dots under appropriate observing conditions. By enhancing the contrast of the very bright dots using an image processing technique, partially ordered long-period superstructures were clearly characterized. For the short-range order state, A₄B, A₂B and A₃B type ordered-clusters are generated in the Ti-rich (002) layers. These ordered-clusters are in contact with each other, and form local microdomains of various superstructures, such as Al ₅Ti₃, h-Al₂Ti and so on. For the Al ₅Ti₃ and h-Al₅Ti ordered states, the ordered-clusters are tiled periodically to form the Al₅Ti ₃ or h-Al₂Ti domains and characteristic anti-phase boundary structures.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures of long-period ordered TiAl alloys that are rich in Al were investigated by the semi-quantitative high-resolution transmission electron microscopy (HRTEM). Local ordered arrangements of Al atoms in (002) Ti-rich layers of the L 1₀ matrix were identified from arrangements of very bright dots in the HRTEM images after appropriate image processing. For a short-range order (SRO) state, the Al atoms form three types of ordered-clusters: square (Ti₄Al), fat rhombus (Ti₃Al) and lean rhombus (Ti₂Al). These clusters are arranged periodically in a short-range to form microdomains of various long-period superstructures: Al₅Ti₃, h-Al₂Ti and so on. Below or above the temperature range showing the SRO state, the Al₅Ti₃ or h-Al₂Ti type cluster-arrangements selectively develop into their long-range order (LRO) domains. Some of the other cluster-arrangements are left between the LRO domains as anti-phase boundary structures.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Formation of anti-phase boundaries (APBs) in the Al₅Ti₃ long-period superstructure of Al-rich TiAl single crystals was examined by the high-resolution transmission electron microscopy (HRTEM) with image processing. The APBs were analyzed focusing on the unique units of ordered clusters such as Ti₄Al, Ti₃Al and Ti₂Al which form square, fat rhombus and lean rhombus shapes in (002) Ti-rich layers, respectively. The Al₅Ti₃-type anti-phase domains (APDs) with various sizes in diameter were obtained in Ti-62.5at.%Al crystals by heat treatment at 600°C or 750°C after the floating zone melting and the subsequent quenching from 1200°C. Almost all the Al₅Ti₃-type APBs lay on {110) and were geometrically classified into 19 types named Type A to Type S. Indeed, 6 types of APBs (Type A to Type F) composed of the units of Ti₄Al, Ti₃Al and Ti₂Al were found, but the other 13 types (Type G to Type S) were not clearly observed. Moreover, a specific type called Type A among the APBs was preferentially formed even in the initial stage of the APD growth. The APBs of Type A appeared with a quite higher frequency than those ideally formed by the random-nucleation and subsequent bounding of APDs. Thus, the APBs of Type A must be already introduced in the stage for nucleation of the APDs and grow stably on {110) due to the quite low APB energy in the long-period superstructure with a relatively large unit cell.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The atomic arrangements of short-range order (SRO) in two Al-rich γ-TiAl alloys with 62.5 and 60.0 at.% Al respectively have been investigated by high-resolution transmission electron microscopy with image processing. For both alloys, SRO structures are formed in Ti-rich (002) layers of the Ll₀ ordered γTiAl matrix, in the course of the phase transformation from the Al₅Ti₃ long-period superstructure phase at lower temperatures to the h-Al₂Ti phase at higher temperatures. The SRO structures are composed of three types of ordered cluster: Ti₄Al type (square shaped), Ti₃Al type (fat rhombus shaped) and Ti₂Al type (lean rhombus shaped). The ordered clusters form local microdomains of the Al₅Ti₃ and Al₃Ti₂ superstructures in addition to the Al₅Ti₃ and h-Al₂Ti superstructures, by different methods of tiling the ordered clusters. Such ordered clusters or microdomains tend to be in contact with each other through common (310) boundaries. This results in peculiar diffuse streaks in diffraction connecting intensity maxima arising from the long-period superstructures.

DOI： 10.1080/09500830210137425

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The atomic arrangements of short-range order (SRO) in two Al-rich gamma-TiAl alloys with 62.5 and 60.0 at.% Al respectively have been investigated by high-resolution transmission electron microscopy with image processing. For both alloys, SRO structures are formed in Ti-rich (002) layers of the L1(0) ordered gamma-TiAl matrix, in the course of the phase transformation from the Al5Ti3 long-period superstructure phase at lower temperatures to the h-Al2Ti phase at higher temperatures. The SRO structures are composed of three types of ordered cluster: Ti4Al type (square shaped), Ti3Al type (fat rhombus shaped) and Ti2Al type (lean rhombus shaped). The ordered clusters form local microdomains of the Al5Ti3&#039; and Al3Ti2 superstructures in addition to the Al5Ti3 and h-Al2Ti superstructures, by different methods of tiling the ordered clusters. Such ordered clusters or microdomains tend to be in contact with each other through common {310) boundaries. This results in peculiar diffuse streaks in diffraction connecting intensity maxima arising from the long-period superstructures.<br />

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Modern high resolution transmission electron microscopy was employed in study of short range order (SRO) in fec-based Ni-Mo, which is classified as '1 1/2 0 alloy'. Digital processing of high resolution transmission electron microscope (HRTEM) images can give information about local atomic arrangements of SRO as well as their projection views. The HRTEM observation with image processing reveals the SRO structures in Ni-Mo depending upon the alloy composition and the heat treatment. Subunit cell clusters of D1_a, DO₂₂ and Pt₂Mo structures are generated in the SRO states of Ni₄Mo and Ni₃Mo alloys. In the initial SRO stales, the number of Pt₂Mo type clusters increases with Mo composition while that of D1_a type decreases. The D1_a, DO₂₂ and Pt₂Mo type clusters increase in number in the early stages of subsequent ordering. The formation of D1_a DO₂₂ and Pt₂Mo type clusters in the SRO states is rationalized in terms of the similar tendencies in atomic configuration between D1_a DO₂₂ and Pt₂Mo structures.

DOI： 10.1016/S0921-5093(00)01872-4

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Nanostructure Formation by Short Range Ordering of Al Atoms in Off-stoichiometric g-TiAl

記述言語：日本語  

Partially ordered Ni₄Mo alloys were observed for the first time at an atomic resolution with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The Mo atomic columns in the D1_a ordered structure were clearly visualized as bright square dots in the HAADF-STEM image. It was found that the ordered regions were observed with a high contrast in the defocus condition a little overfocused from the Scherzer defocus (&Delta;f=sqrtC_S&middot;&lambda;) which is the condition for the smallest electron probe in STEM. The phenomenon was interpreted successfully by using the approximate imaging theory for HAADF-STEM proposed by Jesson et al. Using the present experimental and simulation results, an approximate imaging theory for visualizing short range ordered state in binary alloys, such as the Ni₄Mo alloys, is proposed.

DOI： 10.2320/jinstmet1952.65.5_414

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Partially ordered Ni₄Mo alloys were observed for the first time at an atomic resolution with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The Mo atomic columns in the D1_a ordered structure were clearly visualized as bright square dots in the HAADF-STEM image. It was found that the ordered regions were observed with a high contrast in the defocus condition a little overfocused from the Scherzer defocus (Δf = √C_S · γ) which is the condition for the smallest electron probe in STEM. The phenomenon was interpreted successfully by using the approximate imaging theory for HAADF-STEM proposed by Jesson et al. Using the present experimental and simulation results, an approximate imaging theory for visualizing short range ordered state in binary alloys, such as the Ni₄Mo alloys, is proposed.

DOI： 10.2320/jinstmet1952.65.5_414

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Microstructures of Ti₅₀Al₄₅Mo₅ (at.%) alloy powders produced by the plasma rotating electrode process (PREP) were investigated. The powders have inhomogeneous structures, which consist of dendrites and rounded grains. The dendrites, which show a "rosettelike" morphology, are formed on the powder surface and around the rounded grains. The rosettelike dendrites are of hexagonal α₂ (D0₁₉) phase even though the dendrites have an equiaxial morphology, and a small amount of β₂ (B2) phase is also contained inside. It is suggested that the solidification to α (hcp-A3) phase occurred by the peritectic reaction between the primary β (bcc-A2) dendrites and the liquid: L + β → L + β + α. The rounded grains, on the other hand, are of β₂ phase in which acicular α or α₂ laths are precipitated with the Burgers orientation relationship. Antiphase domain boundaries in the β₂ matrix are intersected by α(α₂) laths. It is interpreted that the α(α₂) laths were formed by the solid-state transformations: β₂ → β₂ + α → β₂ + α₂. The formation of the two different microstructures in the powder particles is rationalized in terms of the changes in local composition of the liquid phase during the rapid solidification process.

DOI： 10.1361/105497101770332938

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The high resolution transmission electron microscope (HRTEM) imaging of short range order (SRO) in Ni₄Mo was investigated by means of multi-slice image simulations. The HRTEM images of Ni₄Mo exhibit locally bright dot patterns corresponding to the [001] projections of the N₂M₂-type (chalcopyrite-like) structure. The multi-slice simulations revealed that the N₂M₂ patterns are rationalized as the projection patterns of the SRO structure which consists of subunit cell clusters of D1(a), D0₂₂ and Pt₂Mo structures. The N₂M₂-type image contrast appears when both the fundamental fcc lattice reflections and the 1 1/2 0 diffuse scattering of SRO contribute enough to imaging. This suggests that a good coincidence in intensity distribution between the Fourier power spectra of HRTEM images and the electron diffraction patterns is one of the conditions for the image contrast of SRO to be interpreted in terms of the projection contrast. (C) 2000 Elsevier Science Ltd.

DOI： 10.1016/S0968-4328(99)00134-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atomic structures of partially ordered Ni-19.5at%Mo alloys are, for the first time, studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The small ordered regions with a D1a structure are clearly visualized as the square-arrangement of bright clots corresponding to the Mo-atomic columns in the dark background due to the disordered matrix with a fcc structure. The variation of the image contrast, where the D1a structure is visualized with high contrast in overfocused conditions from the Scherzer defocus, is observed, which is interpreted by using the approximate imaging theory by Jesson et al. and the size-variation of the probe. The imaging theory for the HAADF-STEM of short-range ordered state in binary alloys is formulated, where the dynamical diffraction effect is reduced in comparison with that for transmission electron microscopy (TEM).

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The short range ordered (SRO) structure in Ni₄Mo has been investigated by means of high resolution transmission electron microscopy with digital image processing and Monte Carlo simulation. High resolution transmission electron microscope (HRTEM) images were recorded with an Imaging Plate (IP) system. Conventionally printed images of the SRO state exhibit locally dot patterns corresponding to N₂M₂-type (chalcopyrite-like) structure. However, the dot patterns transform into those of subunit cell clusters of D1_a, D0₂₂ and Pt₂Mo structures, when the image is output with a different gray scale. The Monte Carlo simulation with appropriate interaction parameters of atoms has explained successfully the HRTEM images. It is concluded that the SRO state in Ni₄Mo involves subunit cell clusters of D1_a, D0₂₂ and Pt₂Mo structures in the atomistic level of microstructure. The concept of 〈11/20〉* static concentration waves corresponding to the N₂M₂ pattern is rationalized as a mesoscopically averaging view of the SRO state.

DOI： 10.1016/S1359-6454(98)00180-3

記述言語：英語   掲載種別：研究論文（学術雑誌）  

High resolution transmission electron microscope (HRTEM) image contrast of short-range order (SRO) in Ni4Mo alloys has been investigated by means of multi-slice simulations. The HRTEM image contrast of SRO in Ni4Mo coincides with a projection contrast of an SRO structure which involves D1(a), D0(22) and Pt2Mo-type subunit cells in a disordered matrix. Multi-slice simulations revealed that the SRO structure exhibit a projection contrast in the HRTEM Image when the fundamental fee lattice reflections contribute sufficiently to HRTEM imaging. The results indicate that the image of SRO in Ni4Mo can be interpreted in terms of projected potential of atomic columns under an appropriate imaging condition.

DOI： 10.2320/matertrans1989.39.914

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The short range ordered (SRO) state and the time-evolution of the long range ordered (LRO) structure of D1_a in a Ni₄Mo alloy were investigated by Monte Carlo simulation based on an f.c.c. Ising model and by transmission electron microscopy (TEM). The simulation using appropriate values for pairwise atomic interactions up to the fifth nearest neighbors bears diffuse intensity maxima at {1 1/2 0} positions in the Fourier power spectrum for the early stage of SRO, and then the maxima shift to {4/5 2/5 0} for the stable Dla structure as the long range ordering proceeds. The present results are in good agreement with the temporal change in electron diffraction due to the SRO-LRO transition in a quenched Ni₄Mo. The SRO state obtained in the simulation contains microclusters of subunit cells of D1_a, D0₂₂ and Pt₂Mo structures. If such a mixed state of microclusters is projected onto a two-dimensional {100} plane in a similar way to high resolution TEM, the mixed state exhibits locally a dot-pattern analogous to the projected N₂M₂-type (chalcopyrite-like) structure, which gives rise to superlattice reflections at {1 1/2 0}. This suggests that a statistically averaging view of the mixture of microclusters leads to the concept of static concentration waves of k = 1 1/2 0, which has been often employed to describe the SRO state. The formation of D0₂₂ and Pt₂Mo-type subunit cells in addition to stable D1_a is explained in terms of their structural relationship. The transformation from SRO to LRO is attributed to continuous growth of D1_a segments into ordered domains.

DOI： 10.1016/S1359-6454(97)00314-5

記述言語：英語   掲載種別：研究論文（学術雑誌）  

High resolution transmission electron microscope (HRTEM) image contrast of short-range order (SRO) in Ni₄Mo alloys has been investigated by means of multi-slice simulations. The HRTEM image contrast of SRO in Ni₄Mo coincides with a projection contrast of an SRO structure which involves D1_a, D0₂₂ and Pt₂Mo-type subunit cells in a disordered matrix. Multi-slice simulations revealed that the SRO structure exhibit a projection contrast in the HRTEM image when the fundamental fcc lattice reflections contribute sufficiently to HRTEM imaging. The results indicate that the image of SRO in Ni₄Mo can be interpreted in terms of projected potential of atomic columns under an appropriate imaging condition.

DOI： 10.2320/matertrans1989.39.914

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The Monte Carlo simulations were carried out to clarify the ordering mechanisms in fcc-based Ni-Mo alloys of Ni₄Mo, Ni₃Mo and Ni₂Mo. When the pairwise atomic interactions up to the eighth coordinate shells are taken into account, the simulation results are consistent with the experimental changes in electron diffraction pattern during the ordering processes in Ni₄Mo, Ni₃Mo and Ni₂Mo alloys. In the early stage of ordering, subunit cell clusters of D1_a, D0₂₂ and Pt₂Mo structures are first generated to form the short range ordered (SRO) state. The selective growth of stable D1_a and/or Pt₂Mo-type ordered domains is involved in the transition to the long range ordered (LRO) state in the following stage.

DOI： 10.2320/matertrans1989.39.133

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The Monte Carlo method of simulation was employed in the study of time-evolution of atomic long-range ordering with k* = 1/2 1/2 1/2 in an fcc Ising-model system with first- and second-neighbor pairwise interactions V(1) and V(2). The results should refer to the ordering behavior of carbon atoms and vacancies in metalloid-deficient transition-metal monocarbides, such as TiC_1-x and NbC_1-x. Fourier power spectra of the obtained atom-configuration involve diffuse streaks in the early stage of the ordering process, and then exhibit sharp spots at k* = 1/2 1/2 1/2 and its equivalent positions in the late stage. When V(1) has a tendency to create unlike-atom pairs in a similar way to V(2), the spectra in the early stage resemble diffraction patterns of TiC_1-x and NbC_1-x with short-range order. Warren-Cowley parameters α's for atomic pair-correlations increase monotonically with time in even-order coordination shells, suggesting continuous evolution of the 1/2 1/2 1/2-type ordering. In contrast, the values of α for odd-order coordination shells first get enhanced with time and then decrease after reaching a peak. The behavior of odd-order α's is explained in terms of the destructive interference (or frustration) between interactions V(1) and V(2). Two different ordered structures of CuPt (R3m) and cubic (Fd3m) types, which are degenerate in the internal energy, simultaneously appear and their ordered domains grow with time.

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