記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語  

DOI： 10.1002/anie.202414786

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記述言語：英語   出版者・発行元：Nano Letters  

An advanced materials solution utilizing the concept of “smart catalysts” could be a game changer for today’s automotive emission control technology, enabling the efficient use of precious metals via their two-way switching between metallic nanoparticle forms and ionic states in the host perovskite lattice as a result of the cyclical oxidizing/reducing atmospheres. However, direct evidence for such processes remains scarce; therefore, the underlying mechanism has been an unsettled debate. Here, we use advanced scanning transmission electron microscopy to reveal the atomic-scale behaviors for a LaFe0.95Pd0.05O3-supported Ir-Pd-Ru nanocatalyst under fluctuating redox conditions, thereby proving the reversible dissolution/exsolution for Ir and Ru but with a limited occurrence for Pd. Despite such selective dissolution during oxidation, all three elements remain cooperatively alloyed in the subsequent reduction, which is a key factor in preserving the catalytic activity of the ternary nanoalloy while displaying its self-regenerating functionality and control of particle agglomeration.

DOI： 10.1021/acs.nanolett.4c03356

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

Amorphous materials are very attractive materials because of their unique properties, including high corrosion resistance and catalytic activity. Creating such materials on a nanoscale is very effective in maximizing their performance. However, it is difficult to synthesize amorphous nanomaterials by conventional rapid cooling methods, commonly used for bulk amorphous materials. Therefore, there are not as many reports about amorphous nanomaterials as bulk materials. Herein we report the first synthesis of Pd–Pt–P amorphous nanoparticles by a 2-step synthesis method. They were also characterized.

DOI： 10.1093/chemle/upae144

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その他リンク： https://academic.oup.com/chemlett/article-pdf/53/8/upae144/58737849/upae144.pdf

記述言語：英語   出版者・発行元：Small Methods  

Electron tomography based on scanning transmission electron microscopy (STEM) is used to analyze 3D structures of metal nanoparticles on the atomic scale. However, in the case of supported metal nanoparticle catalysts, the supporting material may interfere with the 3D reconstruction of metal nanoparticles. In this study, a deep learning-based image inpainting method is applied to high-angle annular dark field (HAADF)–STEM images of a supported metal nanoparticle to predict and remove the background image of the support. The inpainting method can separate an 11 nm Pd nanoparticle from the θ-Al2O3 support in HAADF–STEM images of the θ-Al2O3-supported Pd catalyst. 3D reconstruction of the extracted images of the Pd nanoparticle reveals that the Pd nanoparticle adopts a deformed structure of the cuboctahedron model particle, resulting in high index surfaces, which account for the high catalytic activity for methane combustion. Using the xyz coordinate of each Pd atom, the local Pd–Pd bond distance and its variance in a real supported Pd nanoparticle are visualized, showing large strain and disorder at the Pd–Al2O3 interface. The results demonstrate that 3D atomic-scale analysis enables atomic structure-based understanding and design of supported metal catalysts.

DOI： 10.1002/smtd.202301163

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Sustainable Energy and Fuels  

To realize a carbon-neutral society, developing highly active and inexpensive catalysts for ammonia (NH3) production working under moderate conditions (<400 °C, <10 MPa) using hydrogen fabricated from the electrolysis of water is demanded. Current industrial fused iron (Fe) catalysts show deficient activity under such conditions. Although Ru-based catalysts have been introduced as highly efficient catalysts working under desired conditions, they are scarce and consequently expensive. This work introduces Fe/Ba/MgO (reduced at 700 °C) as an active catalyst with a high ammonia production rate working at mild temperature and pressure (350 °C, 1.0 MPa). Ba doping to Fe nanoparticles supported on MgO and pre-reduction at high temperatures dramatically ameliorated the NH3 production rate. Due to the absence of hydrogen poisoning, the catalytic activity of the Fe/Ba/MgO increased gradually by raising the pressure from 0.1 to 3.0 MPa. The activity of this catalyst at 3.0 MPa was higher than that of two benchmark Ru catalysts. After pre-reduction at high temperature, electrons are donated from the BaO encapsulating the Fe0 nanoparticles to the N2 molecule, which promotes the rate-determining step of ammonia synthesis. We anticipate that these findings will contribute to developing inexpensive Fe catalysts for decarbonizing the ammonia synthesis process to achieve a carbon-neutral society.

DOI： 10.1039/d4se00411f

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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：Chemical Science  

Solid-solution alloys based on platinum group metals and p-block metals have attracted much attention due to their promising potential as materials with a continuously fine-tunable electronic structure. Here, we report on the first synthesis of novel solid-solution RuSn alloy nanoparticles (NPs) by electrochemical cyclic voltammetry sweeping of RuSn@SnOx NPs. High-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy maps confirmed the random and homogeneous distribution of Ru and Sn elements in the alloy NPs. Compared with monometallic Ru NPs, the RuSn alloy NPs showed improved hydrogen evolution reaction (HER) performance. The overpotentials of Ru0.94Sn0.06 NPs/C and Ru0.87Sn0.13 NPs/C to achieve a current density of 10 mA cm−2 were 43.41 and 33.19 mV, respectively, which are lower than those of monometallic Ru NPs/C (53.53 mV) and commercial Pt NPs/C (55.77 mV). The valence-band structures of the NPs investigated by hard X-ray photoelectron spectroscopy demonstrated that the d-band centre of RuSn NPs shifted downward compared with that of Ru NPs. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure analyses indicated that in the RuSn alloy NPs, charge transfer occurs from Sn to Ru, which was considered to result in a downward shift of the d-band centre in RuSn NPs and to regulate the adsorption energy of intermediate Hads effectively, and thus enable the RuSn solid-solution alloy NPs to exhibit excellent HER catalytic properties.

DOI： 10.1039/d3sc06786f

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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 properties of solids could be largely affected by their crystal structures. We achieved, for the first time, the phase control of solid-solution RuIn nanoparticles (NPs) from face-centred cubic (fcc) to hexagonal close-packed (hcp) crystal structures by hydrogen heat treatment. The effect of the crystal structure of RuIn alloy NPs on the catalytic performance in the hydrogen evolution reaction (HER) was also investigated. In the hcp RuIn NPs, enhanced HER catalytic performance was observed compared to the fcc RuIn NPs and monometallic Ru NPs. The intrinsic electronic structures of the NPs were investigated by valence-band X-ray photoelectron spectroscopy (VB-XPS). The d-band centre of hcp RuIn NPs obtained from VB-XPS was deeper than that of fcc RuIn NPs and monometallic Ru NPs, which is considered to enable the hcp RuIn NPs to exhibit enhanced HER catalytic performance.

DOI： 10.1039/d4nr00562g

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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）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

We report the synthesis of novel RuIn solid-solution alloy nanoparticles (NPs) via the electrochemical cleaning of RuIn@InOx NPs. By alloying In to Ru, the RuIn NPs exhibited enhanced hydrogen evolution reaction (HER) activity compared with monometallic face-centered cubic (fcc) Ru NPs. Furthermore, the HER activity of RuIn NPs was comparable to that of commercial Pt catalysts. At a current density of 10 mA cm-2, RuIn NPs displayed a lower overpotential of 30.7 mV compared to monometallic fcc Ru NPs (57.8 mV) and commercial Pt NPs/C (34.1 mV). X-ray photoelectron spectroscopy and X-ray absorption near edge structure analysis revealed charge transfer from In to Ru in RuIn NPs. The results indicate that the alloying of In with Ru leads to beneficial intermetallic charge transfer, which efficiently modulates the desorption energy barrier to intermediate H* and enhances the intrinsic HER performance of monometallic fcc Ru NPs.

DOI： 10.1021/acsmaterialslett.3c01218

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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）  

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）  

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）  

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

The use of nanotubes in the solution state is crucial not only for the exploration of physical and chemical behaviors at the molecular level but also for application such as thin-film fabrication. Surface modification is generally used to solubilize carbon nanotubes (CNTs) and various synthetic nanotubes; however, this method may affect the surface properties of the original nanotubes, and the detailed crystal structure obtained after modification is unclear. Here, we report the synthesis of a crystalline and soluble metal-organic nanotube consisting of a cationic tubular framework and an anion with a long alkyl chain. The nanotubular structures are formed not only in the solid state but also in the solution state, as confirmed by an X-ray structural analysis, optical measurements, and electron microscopy studies. This nanotube system is realized in different states without any surface modification, which is quite different from typical CNTs and synthetic nanotubes. In addition, self-assembled crystalline bundles are directly observed using transmission electron microscopy (TEM) for the first time in a metal-organic nanotube system. The bundle structures are also confirmed by atomic force microscopy (AFM) observations of thin nanotube films. We envisage a systematic design of such soluble metal-organic nanotubes that will enable direct observation of mass transport behavior in channels of bundles or a single nanotube, as well as a wide range of thin-film applications.

DOI： 10.1021/jacs.3c02252

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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：Small  

Highly efficient thermoelectric materials require, including point defects within the host matrix, secondary phases generating positive effects on lowering lattice thermal conductivity (κL). Amongst effective dopants for a functional thermoelectric material, SnTe, Cu doping realizes the ultra-low κL approaching the SnTe amorphous limit. Such effective κL reduction is first attributed to strong phonon scattering by substitutional Cu atoms at Sn sites and interstitial defects in the host SnTe. However, other crystallographic defects in secondary phases have been unfocused. Here, this work reports micro- to atomic-scale characterization on secondary phases of Cu-doped SnTe using advanced microscopes. It is found that Cu-rich secondary phases begin precipitation ≈1.7 at% Cu (x = 0.034 where Sn1−xCuxTe). The Cu-rich secondary phases encapsulate two distinct solids: Cu2SnTe3 ((Formula presented.)) has semi-coherent interfaces with SnTe ((Formula presented.)) such that they minimize lattice mismatch to favor the thermoelectric transport; the other resembles a stoichiometric Cu2Te model, yet is so meta-stable that it demonstrates not only various defects such as dislocation cores and ordered/disordered Cu vacancies, but also dynamic grain-boundary migration with heating and a subsequent phase transition ≈350 °C. The atomic-scale analysis on the Cu-rich secondary phases offers viable strategies for reducing κL through Cu addition to SnTe.

DOI： 10.1002/smll.202204225

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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：ChemCatChem  

Supported Ru catalysts were prepared by using different Ru precursors and examined for the hydrogenation of benzaldehyde to CHM. The catalyst prepared from Ru3(CO)12 precursor and HT support exhibited high yield of CHM. Moderate acidic and basic nature of HT was favourable to control the selectivity for CHM. The physicochemical properties analysis revealed that highly dispersed Ru nanoparticles were effective for the hydrogenation of benzaldehyde. RuCO/HT catalyst was tolerant to different functional groups and was stable until 7th cycle of recycle study.

DOI： 10.1002/cctc.202200241

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出版者・発行元：Journal of the American Chemical Society  

High-entropy alloy nanoparticles (HEA NPs) emerged as catalysts with superior performances that are not shown in monometallic catalysts. Although many kinds of synthesis techniques of HEA NPs have been developed recently, synthesizing HEA NPs with ultrasmall particle size and narrow size distribution remains challenging because most of the reported synthesis methods require high temperatures that accelerate particle growth. This work provides a new methodology for the fabrication of ultrasmall and homogeneous HEA NPs using a continuous-flow reactor with a liquid-phase reduction method. We successfully synthesized ultrasmall IrPdPtRhRu HEA NPs (1.32 ± 0.41 nm), theoretically each consisting of approximately 50 atoms. This average size is the smallest ever reported for HEA NPs. All five elements are homogeneously mixed at the atomic level in each particle. The obtained HEA NPs marked a significantly high hydrogen evolution reaction (HER) activity with a very small 6 mV overpotential at 10 mA/cm-2 in acid, which is one-third of the overpotential of commercial Pt/C. In addition, although mass production of HEA NPs is still difficult, this flow synthesis can provide high productivity with high reproducibility, which is more energy efficient and suitable for mass production. Therefore, this study reports the 1 nm-sized HEA NPs with remarkably high HER activity and establishes a platform for the production of ultrasmall and homogeneous HEA NPs.

DOI： 10.1021/jacs.2c02755

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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：ACS Omega  

Ruthenium catalysts may allow for realization of renewable energy-based ammonia synthesis processes using mild reaction conditions (<400 °C, <10 MPa). However, ruthenium is relatively rare and therefore expensive. Here, we report a Co nanoparticle catalyst loaded on a basic Ba/La2O3support and prereduced at 700 °C (Co/Ba/La2O3_700red) that showed higher ammonia synthesis activity at 350 °C and 1.0-3.0 MPa than two benchmark Ru catalysts, Cs+/Ru/MgO and Ru/CeO2. The synthesis rate of the catalyst at 350 °C and 1.0 MPa (19.3 mmol h-1g-1) was 8.0 times that of Co/Ba/La2O3_500red and 6.9 times that of Co/La2O3_700red. The catalyst showed ammonia synthesis activity at temperatures down to 200 °C. Reduction at the high temperature induced the formation of BaO-La2O3nanofractions around the Co nanoparticles by decomposition of BaCO3, which increased turnover frequency, inhibited the sintering of Co nanoparticles, and suppressed ammonia poisoning. These strategies may also be applicable to other non-noble metal catalysts, such as nickel.

DOI： 10.1021/acsomega.2c01973

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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

The crystal structure significantly affects the physical and chemical properties of solids. However, the crystal structure-dependent properties of alloys are rarely studied because controlling the crystal structure of an alloy at the same composition is extremely difficult. Here, for the first time, we successfully demonstrate the synthesis of binary Ru-Pt (Ru/Pt = 7:3) and Ru-Ir (Ru/Ir = 7:3) and ternary Ru-Ir-Pt (Ru/Ir/Pt = 7:1.5:1.5) solid-solution alloy nanoparticles (NPs) with well-controlled hexagonal close-packed (hcp) and face-centered cubic (fcc) phases, through the chemical reduction method. The crystal structure control is realized by precisely tunning the reduction speeds of the metal precursors. The effect of the crystal structure on the catalytic performance of solid-solution alloy NPs is systematically investigated. Impressively, all the hcp alloy NPs show superior electrocatalytic activities for the hydrogen evolution reaction in alkaline solution compared with the fcc alloy NPs. In particular, hcp-RuIrPt exhibits extremely high intrinsic (mass) activity, which is 3.1 (3.2) and 6.7 (6.9) times enhanced compared to that of fcc-RuIrPt and commercial Pt/C.

DOI： 10.1021/jacs.2c00583

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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：ACS Materials Au  

The crystal structure, which intrinsically affects the properties of solids, is determined by the constituent elements and composition of solids. Therefore, it cannot be easily controlled beyond the phase diagram because of thermodynamic limitations. Here, we demonstrate the first example of controlling the crystal structures of a solid-solution nanoparticle (NP) entirely without changing its composition and size. We synthesized face-centered cubic (fcc) or hexagonal close-packed (hcp) structured PdxRu1-x NPs (x = 0.4, 0.5, and 0.6), although they cannot be synthesized as bulk materials. Crystal-structure control greatly improves the catalytic properties; that is, the hcp-PdxRu1-x NPs exceed their fcc counterparts toward the oxygen evolution reaction (OER) in corrosive acid. These NPs only require an overpotential (η) of 200 mV at 10 mA cm-2, can maintain the activity for more than 20 h, greatly outperforming the fcc-Pd0.4Ru0.6 NPs (η = 280 mV, 9 min), and are among the most efficient OER catalysts reported. Synchrotron X-ray-based spectroscopy, atomic-resolution electron microscopy, and density functional theory (DFT) calculations suggest that the enhanced OER performance of hcp-PdRu originates from the high stability against oxidative dissolution.

DOI： 10.1021/acsmaterialsau.1c00048

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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：Journal of the American Chemical Society  

The compositional space of high-entropy-alloy nanoparticles (HEA NPs) significantly expands the diversity of the materials library. Every atom in HEA NPs has a different elemental coordination environment, which requires knowledge of the local electronic structure at an atomic level. However, such structure has not been disclosed experimentally or theoretically. We synthesized HEA NPs composed of all eight noble-metal-group elements (NM-HEA) for the first time. Their electronic structure was revealed by hard X-ray photoelectron spectroscopy and density function theory calculations with NP models. The NM-HEA NPs have a lower degeneracy in energy level compared with the monometallic NPs, which is a common feature of HEA NPs. The local density of states (LDOS) of every surface atom was first revealed. Some atoms of the same constituent element in HEA NPs have different LDOS profiles, whereas atoms of other elements have similar LDOS profiles. In other words, one atom in HEA loses its elemental identity and it may be possible to create an ideal LDOS by adjusting the neighboring atoms. The tendency of the electronic structure change was shown by supervised learning. The NM-HEA NPs showed 10.8-times higher intrinsic activity for hydrogen evolution reaction than commercial Pt/C, which is one of the best catalysts.

DOI： 10.1021/jacs.1c13616

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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：Catalysis Science and Technology  

Catalytic hydrogenation of nitriles is a cost-effective and green method for synthesizing amines and imines, which have many industrial applications. However, this reaction generally requires harsh reaction conditions and produces a mixture of amine and imine products due to its chemodiversity. Therefore, it is a challenge to selectively hydrogenate nitriles to a single product under ambient conditions (1 bar of H2 at 25 °C). Here, we report an effective method for selective hydrogenation of nitriles that does not require heat, pressurization, or long reaction times. We achieved this by means of bimetalization between palladium (Pd) and platinum (Pt) nanoparticles, which resulted in a catalyst that showed high yield of secondary amines. Although Pd and Pt are thermodynamically immiscible, we have successfully alloyed the two metals by means of rapid chemical reduction assisted by microwave heating. X-ray absorption spectroscopy suggested the formation of heteroatomic Pdδ+Ptδ− sites via charge transfer between neighboring Pd and Pt atoms in the alloy structure. Moreover, Fourier transform IR spectroscopy and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy indicated that decreasing the size of the PdPt (50 : 50) nanoparticles improved the degree of alloying and facilitated the formation of electron-enriched Ptδ− species. On the basis of kinetics studies and density functional theory calculations, we concluded that cyano group activation, which was the rate-determining step over monometallic Pd and Pt catalysts, was accelerated over the heteroatomic Pdδ+Ptδ− sites because of strong back-donation from electron-enriched Ptδ− species to the carbon atom of the cyano groups. The PdPt random alloy nanoparticles catalyzed the reactions of various aromatic and heterocyclic nitriles, and the corresponding secondary amines were selectively obtained in just a few hours.

DOI： 10.1039/d1cy02302k

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Materials and Energy  

The sink strengths of precipitate/matrix interfaces in Cu alloys, were investigated by performing in-situ observation of electron irradiation in high-voltage electron microscopy (HVEM). Fine black spot defects, which seemed to be dislocation loops were observed at irradiation temperature ranging between RT and 373 K in Cu–Cr–Zr, Cu–Cr and GlidCop Al–60 alloys with low number density. In Cu–Cr, loops formed on a part of precipitates interfaces. Hence, a part of precipitate/matrix interfaces is a sink with interstitial bias. Whereas, most of the interfaces are neutral sinks for point defects. In the case of Cu–Cr–Zr and GlidCop Al–60, black spots formed around dislocation, which were induced during two-step heat treatment. The results showed that the precipitate/matrix interface of Cr-rich precipitates in Cu alloys serve as a strong sink for point defects.

DOI： 10.1016/j.nme.2022.101144

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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：Chem Catalysis  

The photocatalytic dry reforming of methane (photoDRM: CH4 + CO2 = 2CO + 2H2) converts greenhouse gases into valuable synthesis gas with photon energy. However, previous photoDRM catalysts comprising supported metal nanoparticles hardly avoid the recombination of photoexcited charges. Herein, we report that significant photoDRM performance can be achieved by a metal-oxide nanocomposite consisting of nanometer-thick, intertwined networks of fibrous rhodium metal and cerium dioxide, i.e., Rh#CeO2. The Rh#CeO2 nanocomposite exhibits the world-highest conversion and yield in photoDRM under UV light irradiation, being accompanied with no other side reactions such as reverse water gas shift reaction. Theoretical simulations and Kelvin probe force microscopy demonstrate that the photoexcited electrons and holes in Rh#CeO2 are efficiently partitioned into the Rh- and CeO2 nanophases, respectively. The efficient charge partitioning in Rh#CeO2 accounts for the selective photoDRM reaction.

DOI： 10.1016/j.checat.2021.11.015

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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：Journal of Physical Chemistry C  

Catalytic oxidation of methane to formaldehyde and methanol has attracted attention because of its advantage in energy efficiency over the conventional multistep reaction process involving endothermic steam reforming of CH4; however, it is challenging to selectively obtain the partial oxidation products in the direct oxidation of CH4. In the present study, Co/SiO2 with various Co loadings was tested for the CH4/O2/H2O gas flow reaction. As a result, Co/SiO2 with a low loading of ≤0.1 wt % showed high selectivity for the partial oxidation reaction and mainly produced HCHO, while Co/SiO2 with high Co loadings proceeded to complete oxidation. Structural analysis using X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and scanning transmission electron microscopy suggested that single Co atoms generated at low Co loadings were effective in the selective oxidation of CH4 to HCHO, while Co3O4 nanoparticles generated at high Co loadings promoted the complete oxidation.

DOI： 10.1021/acs.jpcc.1c08739

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その他リンク： https://doi.org/10.1021/acs.jpcc.1c08739

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/d1sc06578e

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

The Cu6Sn5 intermetallic, which commonly forms at the solder interconnects, is a critical component contributing to the reliability of today's electronic products. It has been established that the structural control of its hexagonal η-Cu6Sn5 polymorph can be achieved over a wide temperature range of service conditions via chemical doping with Ni or Au, effectively suppressing the undesirable hexagonal to monoclinic (ƞ → ƞ′) phase transition at 186 °C and its associated volume change. In this study, we further investigate the effects of Ni (26.5 at%) and Au (9 at%), with high doping/alloying contents, on the atomic-scale structure of η-Cu6Sn5 using a suite of microscopy techniques including atomic-resolution imaging, chemical mapping, electron diffraction, and in-situ heating, coupled with advanced data informatics. Our study reveals that while Ni occupancy takes place in both the Cu1 and Cu2 sites of η-Cu6Sn5 in substantial amounts, Au is mostly substituted at the Cu1 sites of η-Cu6Sn5. Most interestingly, characteristic occupational modulations of the Cu6Sn5 structure arise with each type of dopants: a three-fold ordered structure for Ni accompanied by a displacive modulation of the constituent atoms, but a two-fold layer-like structure for Au. Moreover, with a high content of Ni, the unit cell of η-Cu6Sn5 is found to contract along its hexagonal ah axis relative to the Ni-dilute case, but anisotropically expands the ch axis in a bimodal fashion; in contrast, the effect of Au appears to be of an isotropically expanding nature.

DOI： 10.1016/j.actamat.2021.117513

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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：ACS Nano  

Compositional and structural arrangements of constituent elements, especially those at the surface and near-surface layers, are known to greatly influence the catalytic performance of alloyed nanoparticles (NPs). Although much research effort often focuses on the ability to tailor these important aspects in the design stage, their stability under realistic operating conditions remains a major technical challenge. Here, the compositional stability and associated structural evolution of a ternary iridium-palladium-ruthenium (Ir-Pd-Ru) nanoalloy at elevated temperatures have been studied using interrupted in situ scanning transmission electron microscopy and theoretical modeling. The results are based on a combinatory approach of statistical sampling at the sub-nanometer scale for large groups of NPs as well as tracking individual NPs. We find that the solid solution Ir-Pd-Ru NPs (?5.6 nm) evolved into a Pd-enriched shell supported on an alloyed Ir-Ru-rich core, most notably when the temperature exceeds 500 °C, concurrently with the development of expansive atomic strain in the outer surface and subsurface layers with respect to the core regions. Theoretically, we identify the weak interatomic bonds, low surface energy, and large atomic sizes associated with Pd as the key factors responsible for such observed features.

DOI： 10.1021/acsnano.1c10414

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acscatal.1c02887

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsnano.1c03413

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>We report PtW solid-solution alloy nanoparticles (NPs) as a reverse water-gas shift (RWGS) reaction catalyst for the first time. Atomic-level alloying of Pt and W significantly enhanced the RWGS reaction activity of Pt NPs.</p>

DOI： 10.1039/d1ta03480d

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We first report the facile synthesis of metal-carbon composites consisting of metal nanoparticles (NPs) and different types of carbon species: onion-like and amorphous carbon, Ni@onion-like carbon and Co@amorphous carbon. By simply changing the metal species in an isostructural metal-organic framework, thermal decompositions of MOF-74 directly afforded different types of metal NPs and carbon composites, which exhibited good electrical conductivity. In particular, the Ni@onion-like carbon, having a well-ordered carbon structure, had high electrical conductivity (sigma = 5.3 omega(-1) cm(-1) at 295 K), explained by a modified model of the Efros-Shklovskii variable range hopping.

DOI： 10.1039/d1cc02154k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We present a new synthetic approach for Cu-Pd-B nanoscale alloys. Crystalline face-centered cubic Cu-Pd-B alloy nanoparticles were successfully obtained via an amorphous structure phase caused by external heavy B doping. Elemental mapping with simultaneous energy-dispersive X-ray spectroscopy and energy loss spectroscopy in a scanning transmission electron microscope revealed a solid-solution structure composed of the three elements.

DOI： 10.1246/cl.200861

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Since 1970, people have been making every endeavor to reduce toxic emissions from automobiles. After the development of a three-way catalyst (TWC) that concurrently converts three harmful gases, carbon monoxide (CO), hydrocarbons (HCs), and nitrogen oxides (NOx), Rh became an essential element in automobile technology because only Rh works efficiently for catalytic NOx reduction. However, due to the sharp price spike in 2007, numerous efforts have been made to replace Rh in TWCs. Nevertheless, Rh remains irreplaceable, and now, the price of Rh is increasing significantly again. Here, it is demonstrated that PdRuM ternary solid-solution alloy nanoparticles (NPs) exhibit highly durable and active TWC performance, which will result in a significant reduction in catalyst cost compared to Rh. This work provides insights into the design of highly durable and efficient functional alloy NPs, guiding how to best take advantage of the configurational entropy in addition to the mixing enthalpy.

DOI： 10.1002/adma.202005206

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the synthesis of molybdenum-ruthenium-carbon alloy nanoparticles with molybdenum-rich composition by an annealing treatment following a thermal decomposition. We first found its superconductivity with a transition temperature at around 5 K through the observation of zero resistivity and Meisner effect.

DOI： 10.1246/cl.200779

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the hydrogenation catalytic activity application of molybdenum-ruthenium (MoRu) solid-solution alloy nanoparticles (NPs) as catalysts for the hydrogenation of 1-octene and 1-octyne. The solid-solution structure of MoRu NPs was confirmed through scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX), and powder X-ray diffraction (PXRD) measurement. The hydrogenation catalytic activity of these NPs toward 1-octyne and 1-octene in tetrahydrofuran (THF) was tested. The hydrogenation catalytic activity of Ru was enhanced by alloying with Mo at the atomic level. An electronic modification of Ru by a charge transfer from Mo to Ru, which could induce the change in the adsorption energy of reactants resulting in enhanced catalytic activity, was observed by X-ray photoelectron spectroscopy.

DOI： 10.1002/ejic.202001141

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Water is the only available fossil-free source of hydrogen. Splitting water electrochemically is among the most used techniques, however, it accounts for only 4% of global hydrogen production. One of the reasons is the high cost and low performance of catalysts promoting the oxygen evolution reaction (OER). Here, we report a highly efficient catalyst in acid, that is, solid-solution RuIr nanosized-coral (RuIr-NC) consisting of 3 nm-thick sheets with only 6at.% Ir. Among OER catalysts, RuIr-NC shows the highest intrinsic activity and stability. A home-made overall water splitting cell using RuIr-NC as both electrodes can reach 10mAcm(geo)(-2) at 1.485V for 120h without noticeable degradation, which outperforms known cells. Operando spectroscopy and atomic-resolution electron microscopy indicate that the high-performance results from the ability of the preferentially exposed {0001} facets to resist the formation of dissolvable metal oxides and to transform ephemeral Ru into a long-lived catalyst. Ru is one of the most active metals for oxygen evolution reaction, but it quickly dissolves in acidic electrolyte particularly in nanosized form. Here, the authors show that coral-like solid-solution RuIr consisting of 3 nm-thick sheets with only 6 at% Ir is a long-lived catalyst with high activity.

DOI： 10.1038/s41467-021-20956-4

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Electrooxidation of NH has gained extensive attention for energy and environmental applications such as fuel cells and water purification. In this study, carbon-supported simple metal-nanoparticle, binary- and ternary-nanoalloy (NA) catalysts composed of Fe-group elements, i.e., Fe, Co and Ni, were synthesized and their catalytic performance for NH electrooxidation in alkaline media was investigated. Cyclic voltammetry and chronoamperometry revealed that Ni-containing catalysts show appropriate activities for NH electrooxidation and the catalytic performances of Fe-group catalysts depend on affinity between constituent metals and nitrogen. Each Fe-group element exhibited distinctive catalytic features for the NH electrooxidation, i.e., Ni ensured chemical stability, Fe effectively reduced overpotential and Co increased current density. The ternary NA catalyst showed excellent activities due to combination of all the catalytic features and synergetic effects exerted by the alloying. 3 3 3 3

DOI： 10.1246/bcsj.20210007

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsanm.1c00006

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We report the synthesis of high-entropy-alloy (HEA) nanoparticles (NPs) consisting of five platinum group metals (Ru, Rh, Pd, Ir and Pt) through a facile one-pot polyol process. We investigated the electronic structure of HEA NPs using hard X-ray photoelectron spectroscopy, which is the first direct observation of the electronic structure of HEA NPs. Significantly, the HEA NPs possessed a broad valence band spectrum without any obvious peaks. This implies that the HEA NPs have random atomic configurations leading to a variety of local electronic structures. We examined the hydrogen evolution reaction (HER) and observed a remarkably high HER activity on HEA NPs. At an overpotential of 25 mV, the turnover frequencies of HEA NPs were 9.5 and 7.8 times higher than those of a commercial Pt catalyst in 0.05 M H2SO4 and 1.0 M KOH electrolytes, respectively. Moreover, the HEA NPs showed almost no loss during a cycling test and were much more stable than the commercial Pt catalyst. Our findings on HEA NPs may provide a new paradigm for the design of catalysts.

DOI： 10.1039/d0sc02351e

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>Recyclable Pd_0.5Ru_0.5–PVP catalyst showed higher activity than monometallic Pd or Ru catalyst for the hydrogenation of quinoline. Furthermore, Pd_0.5Ru_0.5–PVP was able to hydrogenate different arenes.</p>

DOI： 10.1039/d0ra09981c

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We report the synthesis of MoRu solid-solution alloy nanoparticles using carbonyl complexes as a precursor through thermal decomposition. Alloying Ru with an early transition metal, Mo, leads to an electronic structure change, resulting in an enhancement of the catalytic activity for the hydrogen evolution reaction, which overtook that of the Pt catalyst.

DOI： 10.1039/d0cc05958g

記述言語：その他   掲載種別：研究論文（学術雑誌）  

<p>This study provides a coreduction methodology for solid solution formation in immiscible systems, with an example of a whole-region immiscible Cu–Ru system.</p>

DOI： 10.1039/d0sc03373a

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/jacs.0c07143

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 American Chemical Society. Quantitative evaluation of the alloying state in nanoalloy systems is key to understanding their functional properties in a diverse range of applications spanning from catalysis and plasmonics to biomedicine and so forth. Here, we develop a method to statistically and visually represent the sub-nanometer local compositional distribution in ternary nanoparticles (NPs) in terms of ternary histograms and kernel density estimation analysis. Further descriptive statistics is performed within the mathematical framework of compositional data analysis to account for the constant-sum constraint and positivity inherent to the nature of compositional data. The approach has been demonstrated on several conceptual particle models and real systems, namely, Pd-Rh-Ru and Ag-Au-Pd NPs, utilizing experimental X-ray energy-dispersive spectroscopy (XEDS) maps acquired from a scanning transmission electron microscope. We regard this as a useful tool for extending to other well-known configurations such as uniformly mixed solid solutions, core-shell, or phase-decomposed clusters often encountered in other nanoalloy systems. Proposed solutions to overcome common problems associated with NPs such as low X-ray counting and XEDS spectral overlapping are also presented and discussed.

DOI： 10.1021/acs.jpcc.0c06813

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 The American Ceramic Society Damaged structures in the MgAl2O4 spinel induced by swift heavy ions were investigated using the X-ray absorption near edge structure (XANES) and small angle X-ray scattering (SAXS). Increasing the fluence of 100 MeV Xe ions leads to increased SAXS intensity and XANES spectral changes on both Mg and Al K-edges. The damaged regions of ion tracks were observed by SAXS to be cylindrical in shape with a diameter of 5 nm. The theoretical XANES spectra indicated that the changes in the experimental spectra were due to the cationic disordering between tetrahedral and octahedral sites. This disordering caused an increase in the inversion degree of the cations. Furthermore, the quantitative analysis of the XANES spectra revealed the preferential occupation of cations at the octahedral sites at high fluence.

DOI： 10.1111/jace.17101

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 American Chemical Society. The platinum-group metals (PGMs) are six neighboring elements in the periodic table of the elements. Each PGM can efficiently promote unique reactions, and therefore, alloying PGMs would create ideal catalysts for complex or multistep reactions that involve several reactants and intermediates. Thus, high-entropy-alloy (HEA) nanoparticles (NPs) of all six PGMs (denoted as PGM-HEA) having a great variety of adsorption sites on their surfaces could be ideal candidates to catalyze complex reactions. Here, we report for the first time PGM-HEA and demonstrate that PGM-HEA efficiently promotes the ethanol oxidation reaction (EOR) with complex 12-electron/12-proton transfer processes. PGM-HEA shows 2.5 (3.2), 6.1 (9.7), and 12.8 (3.4) times higher activity than the commercial Pd/C, Pd black and Pt/C catalysts in terms of intrinsic (mass) activity, respectively. Remarkably, it records more than 1.5 times higher mass activity than the most active catalyst to date. Our findings pave the way for promoting complex or multistep reactions that are seldom realized by mono- or bimetallic catalysts.

DOI： 10.1021/jacs.0c04807

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 American Physical Society. Chemical modification using only small amounts of elements such as Zn, In, Sb, or Ni has proven to be an effective means to control the desirable crystal structure of hexagonal η-Cu6Sn5 over a wide thermally operating window, typically found in Pb-free Sn-based soldering or Li-ion battery anode applications. Though appealing, the underlying mechanisms on the role of these dopants remain incomplete and their atomic arrangements within the η-Cu6Sn5 lattices have not yet been experimentally determined. In the current study, we directly reveal the atomic positions of Zn, In, and Sb at the Sn sites of η-Cu6Sn5 via atomic-scale x-ray energy dispersive spectroscopy (XEDS) maps utilizing advanced Cs-corrected scanning transmission electron microscopy. The use of advanced statistical algorithms including Poisson non-local principal component analysis and lattice averaging enables the fine resolution of weak XEDS maps from trace dopant elements. Our first-principles calculations further identify the influence of dopants at these atomic sites on the overall energetics, electronic structures, as well as local bonding environments, leading to the most favorable situations for η-Cu6Sn5 stabilization.

DOI： 10.1103/PhysRevMaterials.4.065002

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ammonia is a potential carrier of hydrogen as a zero-emission fuel. Herein, the effects of calcination and reduction temperatures on the ammonia-synthesis activity of Ru/La0.5Ce0.5O1.75 are investigated under mild synthesis conditions (≤400 °C, ≤3 MPa), which are the preferred conditions for the storage of hydrogen as an energy source. The highest catalytic activity is obtained after calcination of the support at 700 °C and reduction of the catalyst at 650 °C. Calcination using a higher temperature than that used for reduction results in the induction of a strong metal–support interaction (SMSI) effect. This high-temperature calcination also provides heat resistance to the support, which prevents sintering of the primary support particles during reduction. Thus, calcination and reduction at temperatures higher than those normally used for the preparation of Ru catalysts provide a novel approach for obtaining supported highly dispersed Ru catalysts exhibiting the SMSI effect and high catalytic activities.

DOI： 10.1002/ente.202000264

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© The Royal Society of Chemistry. We report the significantly enhanced CO oxidation activity of Pd nanoparticles covered with [Zr6O4(OH)4(BDC)6] (UiO-66, BDC = 1,4-benzenedicarboxylate). The catalytic activity was much higher than those of Pd and Ru nanoparticles on ZrO2. The origin of the enhancement was suggested to be a change in the CO adsorption properties on Pd nanoparticles.

DOI： 10.1039/d0cc00566e

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Dry reforming of methane is one of the key reactions to exploit natural gas feedstocks by their catalytic conversion to synthesis gas (CH4 + CO2 → 2H2 + 2CO), which is used in the production of transportable liquid fuel. However, this reaction suffers from thermodynamic conversion limits and high thermal energy requirements. Herein we report that a SrTiO3-supported rhodium (Rh/STO) catalyst efficiently promotes methane reforming under ultraviolet light irradiation without heat supply at low temperatures, which cannot be achieved by conventional thermal catalysis. The photoexcited holes and electrons are used for CH4 oxidation over STO and CO2 reduction over rhodium, respectively. Isotope analysis clarified that the lattice oxygens (O2−) act as mediator to drive dry reforming of methane. The materials design of Rh/STO can be extended in principle to diverse uphill reactions that utilize photon energy to obtain valued products from different carbon resources.

DOI： 10.1038/s41929-019-0419-z

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 American Chemical Society. To mitigate global problems related to energy and global warming, it is helpful to develop an ammonia synthesis process using catalysts that are highly active under mild conditions. Here we show that the ammonia synthesis activity per weight of catalyst of Ru/Ba/LaCeOx, prereduced at 700 °C, is the highest among reported oxide-supported Ru catalysts, 52.3 mmol h-1 gcat-1 at 350 °C, 1.0 MPa. The turnover frequency of Ru/Ba/LaCeOx at 350 °C was more than 8 times that of Cs+/Ru/MgO, which is a well-known active catalyst used as a benchmark; furthermore, hydrogen poisoning, a typical drawback for oxide-supported Ru catalysts, was effectively suppressed. Scanning transmission electron microscopy observations with energy dispersive X-ray spectrometry and electron energy loss spectroscopy analysis revealed that a low-crystalline, oxygen-deficient nanofraction including Ba2+, Ce3+, and La3+ had accumulated on the Ru particles. This unique structure was obtained by exploiting the surface dynamics of alkaline earth compounds and thermostable rare earth oxides that contain redox-active atoms during the reduction at an unusually high temperature. The nanofraction showed strong electron-donating ability because of the strong basicity of the included cations, removal of carbonate, and formation of oxygen defect sites that eliminated electron-withdrawing O2- anions from the interface between the nanofraction and Ru atom. Electrons were therefore effectively donated to antibonding π -orbitals of the N2 molecules via Ru in contact with the nanofraction, and NN triple bond cleavage, which is the rate-determining step for ammonia synthesis, was promoted.

DOI： 10.1021/acssuschemeng.9b06299

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Copyright © 2019 American Chemical Society. Transition metal carbides have attractive physical and chemical properties that are much different from their parent metals. Particularly, noble metal carbides are expected to be promising materials for a variety of applications, particularly as efficient catalysts. However, noble metal carbides have rarely been obtained because carbide phases do not appear in noble metal-carbon phase diagrams and a reasonable synthesis method to make noble metal carbides has not yet been established. Here, we propose a new synthesis method for noble metal carbides and describe the first synthesis of rhodium carbide using tetracyanoethylene (TCNE). The rhodium carbide was synthesized without extreme conditions, such as the very high temperature and/or pressure typically required in conventional carbide syntheses. Moreover, we investigated the electronic structure and catalytic activity for the hydrogen evolution reaction (HER). We found that rhodium carbide has much higher catalytic activity for HER than pure Rh. Our study provides a feasible strategy to create new metal carbides to help advance the field of materials science.

DOI： 10.1021/jacs.9b09219

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019, The Author(s). The triple phase boundary (TPB) of metal, oxide, and gas phases in the anode of solid oxide fuel cells plays an important role in determining their performance. Here we explore the TPB structures from two aspects: atomic-resolution microscopy observation and reaction dynamics simulation. Experimentally, two distinct structures are found with different contact angles of metal/oxide interfaces, metal surfaces, and pore opening sizes, which have not previously been adopted in simulations. Reaction dynamics simulations are performed using realistic models for the hydrogen oxidation reaction (HOR) at the TPB, based on extensive development of reactive force field parameters. As a result, the activity of different structures towards HOR is clarified, and a higher activity is obtained on the TPB with smaller pore opening size. Three HOR pathways are identified: two types of hydrogen diffusion processes, and one type of oxygen migration process which is a new pathway.

DOI： 10.1038/s42004-019-0148-x

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2020 The Chemical Society of Japan | 207 Rh nanoparticles (NPs) with various shapes exposing different faces were synthesized and their catalytic activities for hydrogen evolution reaction (HER) were investigated. Rh NPs showed a shape dependence on the catalytic activities and the activity of Rh NPs with high-index faces was higher than the others.

DOI： 10.1246/cl.190830

記述言語：その他   掲載種別：研究論文（学術雑誌）  

This journal is © The Royal Society of Chemistry. We succeeded in controlling the crystal structure of osmium (Os) nanoparticles (NPs). Although Os adopts only a hexagonal close-packed (hcp) structure in the bulk state, a face-centred cubic (fcc) Os was synthesized by a chemical reduction method using an Os acetylacetonate complex as a precursor.

DOI： 10.1039/c9cc09192k

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim There is interest in minimizing or eliminating the use of Pt in catalysts by replacing it with more widely abundant and cost-effective elements. The alloying of Pt with non-noble metals is a potential strategy for reducing Pt use because interactions between Pt and non-noble metals can modify the catalyst structure and electronic properties. Here, a γ-Al2O3-supported bimetallic catalyst [Pt(0.1)Co(1)/Al2O3] was prepared which contained 0.1 wt % Pt and 1 wt % Co and thus featured an extremely low Pt : Co ratio (<1 : 30 mol/mol). The Pt and Co in this catalyst formed alloy nanoparticles in which isolated electron-rich Pt atoms were present on the nanoparticle surface. The activity of this Pt(0.1)Co(1)/Al2O3 catalyst for the purification of automotive exhaust was comparable to the activities of 0.3 and 0.5 wt % Pt/γ-Al2O3 catalysts. Electron-rich Pt and metallic Co promoted activation of NOx and oxidization of CO and hydrocarbons, respectively. This strategy of tuning the surrounding structure and electronic state of a noble metal by alloying it with an excess of a non-noble metal will enable reduced noble metal use in catalysts for exhaust purification and other environmentally important reactions.

DOI： 10.1002/cplu.201800542

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© 2018 The Author(s). In situ sequential high-resolution observations were performed on gold nanorods under near-infra-red pulsed laser irradiation using a high-voltage electron microscope attached to a pulsed laser illumination system. The original nanorods were single crystals; the longer axes were oriented along [001]. Under laser light irradiation with λ = 1064 nm with an average intensity per pulse of 980 or 490 J/m 2, the shape of the nanorods changed from rod to barrel surrounded by the {111} and {001} facets, while the original single-crystalline structure was maintained. The side surfaces with <110> direction were reconstructed into zig-zag fine structures consisting of narrow {111} facets. The temporal evolution of the volume and surface area during irradiation was evaluated based on the images, assuming that the particles have a rotational symmetry along their longer axes. The surface area was stepwise decreased during the shape change using pulse shots of 980 J/m 2 while the volume was maintained. On the other hand, several repeated shots were required to induce the shape change when the averaged intensity was reduced to 490 J/m 2 per pulse. In addition to the surface area, the volume was reduced under the latter condition during the shape change due to the evaporation of atoms. The quantitative analysis of the temporal changes indicates the heterogeneity of the atomic excitation or heating of gold nanorods induced by pulsed laser illumination.

DOI： 10.1093/jmicro/dfy136

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© 2019 The Royal Society of Chemistry. Au and Ru are elements that are immiscible in the bulk state and have the largest gap in reduction potential among noble metals. Here, for the first time, AuxRu1-x solid-solution alloy nanoparticles (NPs) were successfully synthesized over the whole composition range through a chemical reduction method. Powder X-ray diffraction and scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy showed that Au and Ru atoms are homogeneously mixed at the atomic level. We investigated the catalytic performance of AuxRu1-x NPs for the oxygen evolution reaction, for which Ru is well known to be one of the best monometallic catalysts, and we found that even alloying with a small amount of Au could significantly enhance the catalytic performance.

DOI： 10.1039/c9sc00496c

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© 2019 American Chemical Society. This work is motivated by an interesting phenomenon discovered by Kobayashi et al., whereby a phase-separated nanoparticle of the Pd-core and Pt-shell is mixed into a solid solution alloy nanoparticle by repeating hydrogen absorption/desorption processes at 373 K. To investigate the structural change, including the positions of hydrogen atoms and the thermodynamic aspect, we measured the neutron diffraction and enthalpy of hydrogen absorption for Pd0.8Pt0.2 nanoparticles (diameter: 5.0 ± 1.1 nm). Rietveld and atomic pair distribution function (PDF) analyses revealed that D atoms are located at the interstitial octahedral (O) and tetrahedral (T) sites in the solid solution Pd0.8Pt0.2D0.36 nanoparticles, while D atoms are not located at the interstitial sites but trapped somewhere, probably at the surface and at the core-shell interface, in core-shell Pd0.8Pt0.2D0.50 nanoparticles. These results are consistent with the model in which hydrogen atoms play a role in creating defects around the interface to lower the activation energy of the mixing process. The enthalpies of H2 and D2 absorptions in the solid solution Pd0.8Pt0.2 nanoparticles at 298 K and 0.1 MPa are -(20.7 ± 0.1) kJ(H·mol)-1 and -(20.1 ± 0.2) kJ(D·mol)-1, respectively. Both of these values are larger than the corresponding values in Pd nanoparticles, suggesting that the hydrogen absorption sites are stabilized by adding Pt atoms, even though Pt itself does not absorb hydrogen. This unusual and interesting effect is discussed on the basis of the structural and thermodynamic data obtained in this work.

DOI： 10.1021/acs.jpcc.8b11380

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© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Ru is an important catalyst in many types of reactions. Specifically, Ru is well known as the best monometallic catalyst for oxidation of carbon monoxide (CO) and has been practically used in residential fuel cell systems. However, Ru is a minor metal, and the supply risk often causes violent fluctuations in the price of Ru. Performance-improved and cost-reduced solid-solution alloy nanoparticles of the Cu-Ru system for CO oxidation are now presented. Over the whole composition range, all of the Cu x Ru 1−x nanoparticles exhibit significantly enhanced CO oxidation activities, even at 70 at % of inexpensive Cu, compared to Ru nanoparticles. Only 5 at % replacement of Ru with Cu provided much better CO oxidation activity, and the maximum activity was achieved by 20 at % replacement of Ru by Cu. The origin of the high catalytic performance was found as CO site change by Cu substitution, which was investigated using in situ Fourier transform infrared spectra and theoretical calculations.

DOI： 10.1002/anie.201812325

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© The Royal Society of Chemistry. We report the synthesis and characterization of highly active Cu nanoparticles covered with zirconium/hafnium-based metal-organic frameworks for CO2 hydrogenation to methanol. Compared to Cu/γ-Al2O3, Cu/ZIF-8, Cu/MIL-100 and Cu/UiO-66 composites, UiO-66 acts as the most active support, with Cu/Zr-UiO-66 producing methanol at a rate 70 times higher than that of Cu/γ-Al2O3. In addition, the replacement of Zr4+ with Hf4+ in UiO-66 tripled in the rate of methanol production. Furthermore, we describe a substituent effect on the catalytic activity, with Cu/Zr-UiO66-COOH providing a three-fold enhancement of methanol production, compared to that of Zr-UiO-66 or Zr-UiO66-NH2. The enhanced catalytic activity of Cu nanoparticles depends on the charge transfer degree from Cu nanoparticles to UiO-66 at the interface between Cu nanoparticles and UiO-66.

DOI： 10.1039/c8sc05441j

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© 2019 The Royal Society of Chemistry. CePO4 nanorods with uniform surface Ce sites could work as a durable catalyst and showed the highest C2 yield of 18% in an electric field without the need for external heating, which was comparable to that reported for high-performance catalysts at high temperature (>900 K).

DOI： 10.1039/c9cc00174c

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© 2018 American Chemical Society. To exploit the use of hydrogen as a source of sustainable energy, development of an efficient process for synthesizing an energy carrier such as ammonia under mild conditions will be necessary. Here, we show that Ru/La0.5Pr0.5O1.75 prereduced at an extraordinary high temperature of 650 °C catalyzes high NH3-synthesis rates under mild conditions. At 400 °C under 1.0 MPa, the synthesis rate was comparable with that of most active oxide-supported Ru catalysts. Kinetic analysis revealed that hydrogen poisoning, which is a typical drawback for oxide-supported Ru catalysts such as Cs+/Ru/MgO, was effectively suppressed over Ru/La0.5Pr0.5O1.75. The high activity induced by high-temperature reduction was attributable to the good thermal stability of the support and a phase change of the La0.5Pr0.5O1.75 support during prereduction. Fourier transform-infrared spectroscopy measurements after N2 adsorption on the catalyst revealed that electrons were efficiently donated from trigonal La0.5Pr0.5O1.5 to the antibonding π orbital of the N≡N bond of N2 via Ru atoms. Cleavage of the N≡N bond, the rate-determining step for ammonia synthesis, was thus accelerated. Our results expand the range of possibilities for developing more effective ammonia synthesis catalysts under mild conditions. Such catalysts will be needed to enable development of hydrogen-based sustainable energy resources.

DOI： 10.1021/acssuschemeng.8b04683

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© 2019 The Royal Society of Chemistry. The electronic structure of surface atoms has a great effect on catalytic activity because the binding energy of reactants is closely related to the electronic structure. Therefore, designing and controlling the local density of states (LDOS) of the catalyst surface would be a rational way to develop innovative catalysts. Herein, we first demonstrate a highly active AuIr solid-solution alloy electrocatalyst for the oxygen reduction reaction (ORR) by emulating the Pt LDOS profile. The calculated LDOS of Ir atoms on the Au0.5Ir0.5(111) surface closely resembled that of Pt(111), resulting in suitable oxygen adsorption energy on the alloy surface for the ORR. We successfully synthesized AuIr solid-solution alloys, while Ir and Au are immiscible even above their melting points in the bulk state. Although monometallic Ir or Au is not active for the ORR, the synthesized Au0.5Ir0.5 alloy demonstrated comparable activity to Pt at 0.9 V versus a reversible hydrogen electrode.

DOI： 10.1039/c8sc04135k

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© 2019 The Chemical Society of Japan We report, for the first time, metal (Pd) nanocrystals (NCs) covered with a 2D flexible metalorganic framework (MOF) of [Zn(NO2-ip)(bpy)]n (NO2-ip: 5-nitro-isophthalate, bpy: 4,4¤-bipyridine). The hybrid materials were characterized by powder X-ray diffraction measurements and transmission electron microscope techniques. The CO2 sorption and hydrogen storage properties revealed that both the flexible porous character of the MOF and the hydrogen absorption ability of Pd NCs were compatible in the hybrid.

DOI： 10.1246/cl.180931

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 Elsevier Ltd Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS), and first principles calculations of EEL spectra were utilized to elucidate the relationship between the microscopic structure and the electrochemical properties of heavily boron-doped diamond (h-BDD). The electrochemical properties of h-BDD containing 1 at.% and 3 at.% boron are very different. TEM observations showed that 1 at.% h-BDD consists of small densely packed diamond crystallites, while 3 at.% h-BDD contains small voids and a graphite phase partly along the grain boundaries. The EEL spectrum of the grain interior in 1 at.% h-BDD and comparison of this with a theoretical spectrum shows that the boron atoms are mostly dispersed as single isolated substitutional atoms on diamond lattice sites in the grain interior and that only a small amount of sp2-bonded carbon is present. In contrast, in the grain interior of 3 at.% h-BDD, the boron atoms are mostly associated with nearest neighbor boron pairs, and consequently sp2-bonded carbon is formed. Thus, the local structure has a significant effect on the amount of sp2-bonded carbon. The quite different electrochemical properties of the samples are ascribed to the amount of sp2-bonding arising from the different local structures.

DOI： 10.1016/j.carbon.2018.05.026

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Solid oxide fuel cells (SOFCs) with liquefied petroleum gas (LPG) reduce CO2 emissions due to their high-energy-conversion efficiency. Although SOFCs can convert LPG directly, coking occurs easily by decomposition of hydrocarbons, including C−C bonds on the electrode of fuel cell stacks. It is therefore necessary to develop an active steam pre-reforming catalyst that eliminates the hydrocarbons at low temperature, in which waste heat of SOFCs is used. Herein, we show that the crystal structure of the TiO2 that anchors Rh particles is crucial for catalytic activity of Rh/TiO2 catalysts for propane pre-reforming. Our experimental results revealed that strong metal support interaction (SMSI) induced during H2 pre-reduction were optimized over Rh/TiO2 with a rutile structure; this catalyst catalyzed the reaction much more effectively than conventional Rh/γ-Al2O3. In contrast, the SMSI was too strong for Rh/TiO2 with an anatase structure, and the surface of the Rh particles was therefore covered mostly with partially reduced TiO2. The result was very low activity.

DOI： 10.1002/chem.201800936

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim For the first time, we synthesize solid-solution alloy nanoparticles of Ir and Cu with a size of ca. 2 nm, despite Ir and Cu being immiscible in the bulk up to their melting over the whole composition range. We performed a systematic characterization on the nature of the IrxCu1−x solid-solution alloys using powder X-ray diffraction, scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results showed that the IrxCu1−x alloys had a face-centered-cubic structure; charge transfer from Cu to Ir occurred in the alloy nanoparticles, as the core-level Ir 4f peaks shifted to lower energy region with the increase in Cu content. Furthermore, we observed that the alloying of Ir with Cu enhanced both the electrocatalytic oxygen evolution and oxygen reduction reactions. The enhanced activities could be attributed to the electronic interaction between Ir and Cu arising from the alloying effect at atomic-level.

DOI： 10.1002/anie.201800650

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）  

© 2018 Trans Tech Publications, Switzerland. Cu6Sn5 is an important intermetallic compound in soldering and electronic packaging. It is formed at the interface between molten solder and substrate during the soldering process, and the evolution of microstructure and properties also occurs in service. Previous studies revealed that Au and Ni are stabilization alloying elements for hexagonal η-Cu6Sn5intermetallic. For better understanding of stabilization mechanisms at atomic resolution level, in this work, we made an attempt atomic structure analysis on a stoichiometric (Cu, Au, Ni)6Sn5intermetallic prepared by direct alloying. High-angle annular dark-field (HAADF) imaging and atomic-resolution chemical mapping were taken by the aberration-corrected (Cs-corrected) scanning transmission electron microscopy (STEM). It is found that Au and Ni doped Cu6Sn5has hexagonal structure. The atom sites of Cu1 and Sn can be distinguished in atomic-resolution images after being observed from orientation [2 1 1 0], which is also confirmed by atomic-resolution chemical mapping analysis. Importantly, atomic-resolution about distribution of alloying Au atom was directly observed, and Au atoms occupy the Cu1 sites in η-Cu6Sn5.

DOI： 10.4028/www.scientific.net/SSP.273.95

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 The Royal Society of Chemistry. We report on binary solid-solution nanoparticles (NPs) composed of Pd and Ir, which are not miscible at the equilibrium state of the bulk, for the first time, by means of a process of hydrogen absorption/desorption from core (Pd)/shell (Ir) NPs. Only 20 at&#37; replacement with Ir atoms doubled the hydrogen-storage capability compared to Pd NPs, which are a representative hydrogen-storage material. Furthermore, the systematic control of hydrogen concentrations and the corresponding pressure in Pd and Pd-M NPs (M = Ir, Pt, Au) have been achieved based on the band filling control of Pd NPs.

DOI： 10.1039/c8sc01460d

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Cu6Sn5 is an important intermetallic compound in soldering and electronic packaging. It is formed at the interface between molten solder and substrate during the soldering process, and the evolution of microstructure and properties also occurs in service. Previous studies revealed that Au and Ni are stabilization alloying elements for hexagonal η-Cu₆Sn₅intermetallic. For better understanding of stabilization mechanisms at atomic resolution level, in this work, we made an attempt atomic structure analysis on a stoichiometric (Cu, Au, Ni)₆Sn₅intermetallic prepared by direct alloying. High-angle annular dark-field (HAADF) imaging and atomic-resolution chemical mapping were taken by the aberration-corrected (Cs-corrected) scanning transmission electron microscopy (STEM). It is found that Au and Ni doped Cu₆Sn₅has hexagonal structure. The atom sites of Cu1 and Sn can be distinguished in atomic-resolution images after being observed from orientation [2 1 1 0], which is also confirmed by atomic-resolution chemical mapping analysis. Importantly, atomic-resolution about distribution of alloying Au atom was directly observed, and Au atoms occupy the Cu1 sites in η-Cu₆Sn₅.

DOI： 10.4028/www.scientific.net/SSP.273.95

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2018 The Royal Society of Chemistry. Ammonia is an important feedstock for producing fertiliser and is also a potential energy carrier. However, the process currently used for ammonia synthesis, the Haber-Bosch process, consumes a huge amount of energy; therefore the development of new catalysts for synthesising ammonia at a high rate under mild conditions (low temperature and low pressure) is necessary. Here, we show that Ru/La0.5Ce0.5O1.75 pre-reduced at an unusually high temperature (650 °C) catalysed ammonia synthesis at extremely high rates under mild conditions; specifically, at a reaction temperature of 350 °C, the rates were 13.4, 31.3, and 44.4 mmol g-1 h-1 at 0.1, 1.0, and 3.0 MPa, respectively. Kinetic analysis revealed that this catalyst is free of hydrogen poisoning under the conditions tested. Electron energy loss spectroscopy combined with O2 absorption capacity measurements revealed that the reduced catalyst consisted of fine Ru particles (mean diameter < 2.0 nm) that were partially covered with partially reduced La0.5Ce0.5O1.75 and were dispersed on a thermostable support. Furthermore, Fourier transform infrared spectra measured after N2 addition to the catalyst revealed that N2 adsorption on Ru atoms that interacted directly with the reduced La0.5Ce0.5O1.75 weakened the NN bond and thus promoted its cleavage, which is the rate-determining step for ammonia synthesis. Our results indicate that high-temperature pre-reduction of this catalyst, which consists of Ru supported on a thermostable composite oxide with a cubic fluorite structure and containing reducible cerium, resulted in the formation of many sites that were highly active for N2 reduction by hydrogen.

DOI： 10.1039/c7sc05343f

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cationic disorder in the MgAl₂O₄ spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradiation fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calculated spectra based on density function theory indicate that the change in the experimental spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAl₂O₄ induced by the high density electronic excitation under swift heavy ion irradiation.

DOI： 10.1039/c7cp07591j

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ammonia is an important feedstock for producing fertiliser and is also a potential energy carrier. However, the process currently used for ammonia synthesis, the Haber-Bosch process, consumes a huge amount of energy; therefore the development of new catalysts for synthesising ammonia at a high rate under mild conditions (low temperature and low pressure) is necessary. Here, we show that Ru/La_0.5Ce_0.5O_1.75 pre-reduced at an unusually high temperature (650 °C) catalysed ammonia synthesis at extremely high rates under mild conditions; specifically, at a reaction temperature of 350 °C, the rates were 13.4, 31.3, and 44.4 mmol g^-1 h^-1 at 0.1, 1.0, and 3.0 MPa, respectively. Kinetic analysis revealed that this catalyst is free of hydrogen poisoning under the conditions tested. Electron energy loss spectroscopy combined with O₂ absorption capacity measurements revealed that the reduced catalyst consisted of fine Ru particles (mean diameter < 2.0 nm) that were partially covered with partially reduced La_0.5Ce_0.5O_1.75 and were dispersed on a thermostable support. Furthermore, Fourier transform infrared spectra measured after N₂ addition to the catalyst revealed that N₂ adsorption on Ru atoms that interacted directly with the reduced La_0.5Ce_0.5O_1.75 weakened the NN bond and thus promoted its cleavage, which is the rate-determining step for ammonia synthesis. Our results indicate that high-temperature pre-reduction of this catalyst, which consists of Ru supported on a thermostable composite oxide with a cubic fluorite structure and containing reducible cerium, resulted in the formation of many sites that were highly active for N₂ reduction by hydrogen.

DOI： 10.1039/c7sc05343f

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2017 Acta Materialia Inc. The microstructure in a Mn55.2Ga19.0Cu25.8 alloy that exhibits both martensitic and diffusional phase transformations was examined by electron microscopy, and the potential effects of these transformations on the large coercivity (~ 2 T) were discussed. The alloy showed a cellular microstructure, composed of a cuboidal matrix enveloped by a boundary phase, and superposed on well-defined martensite plates. Since the boundary phase is enriched by the non-magnetic element Cu, it may serve as magnetic isolation for the matrix region with a face centered tetragonal lattice formed by the martensitic transformation, or offer potential pinning sites for magnetic domain walls.

DOI： 10.1016/j.scriptamat.2017.03.013

記述言語：その他  

© The Author(s) 2017. In a comment on our Article "Evidence of the hydrogen release mechanism in bulk MgH2", Surrey et al. assert that the MgH2 sample we studied was not MgH2 at any time but rather MgO; and that the transformation we observed was the formation of Kirkendall voids due to the outward diffusion of Mg. We address these issues in this reply.

DOI： 10.1038/srep43720

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2017 American Chemical Society. We report on novel solid-solution alloy nanoparticles (NPs) of Ru and Cu that are completely immiscible even above melting point in bulk phase. Powder X-ray diffraction, scanning transmission electron microscopy, and energy-dispersive X-ray measurements demonstrated that Ru and Cu atoms were homogeneously distributed in the alloy NPs. Ru0.5Cu0.5 NPs demonstrated higher CO oxidation activity than fcc-Ru NPs, which are known as one of the best monometallic CO oxidation catalysts.

DOI： 10.1021/jacs.7b01186

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2016 Elsevier B.V. Hydrogen storage is an important aspect to enable the so-called hydrogen economy. Mg-Ni alloys are among the most promising candidates for solid-state hydrogen storage systems yet many questions remain unanswered regarding the hydriding/dehydriding mechanism of the alloys. Mg2NiH4 particularly has received much attention both for its potential as a hydrogen storage medium and also exhibits interesting properties relating to its different polymorphs. Here, the dehydriding mechanism in bulk Mg2NiH4 is investigated using in-situ ultra-high voltage transmission electron microscopy (TEM) combined with Synchrotron powder X-ray diffraction (XRPD) and differential scanning calorimetry (DSC). We find that the hydrogen release is based on a mechanism of nucleation and growth of Mg2NiHx (x∼0–0.3) solid solution grains and is greatly enhanced in the presence of crystal defects occurring as a result of the polymorphic phase transformation. Also importantly, with atomic resolution TEM imaging a high density of stacking faults is identified in the dehydrided Mg2NiHx (x∼0–0.3) lattices.

DOI： 10.1016/j.jpowsour.2016.11.105

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The first synthesis of pure Rh1−xCux solid-solution nanoparticles is reported. In contrast to the bulk state, the solid-solution phase was stable up to 750 °C. Based on facile density-functional calculations, we made a prediction that the catalytic activity of Rh1−xCux can be maintained even with 50 at % replacement of Rh with Cu. The prediction was confirmed for the catalytic activities on CO and NOx conversions.

DOI： 10.1002/chem.201604286

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on hexagonal close-packed (hcp) palladium (Pd)–boron (B) nanocrystals (NCs) by heavy B doping into face-centered cubic (fcc) Pd NCs. Scanning transmission electron microscopy–electron energy loss spectroscopy and synchrotron powder X-ray diffraction measurements demonstrated that the B atoms are homogeneously distributed inside the hcp Pd lattice. The large paramagnetic susceptibility of Pd is significantly suppressed in Pd–B NCs in good agreement with the reduction of density of states at Fermi energy suggested by X-ray absorption near-edge structure and theoretical calculations.

DOI： 10.1002/anie.201703209

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Size-controlled Rh nanoparticles stabilized by poly(vinyl-pyrrolidone) were quickly synthesized via alcohol reduction. Microwave-assisted synthesis in closed vessels allowed alcohols with low-to-high boiling points to be used as reductants under the same preparation conditions. Pure ethanol has not been used previously because its boiling point is lower than the temperature required for Rh³⁺ reduction. Alcohols with relatively strong reduction ability were found to lead to smaller Rh nanoparticles. The ability to oxidize CO was enhanced as the Rh particle size decreased.

DOI： 10.1246/cl.170440

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The realization of metal nanoparticles (NPs) with bimetallic character and distinct composition for specific catalytic applications is an intensively studied field. Due to the synergy between metals, most bimetallic particles exhibit unique properties that are hardly provided by the individual monometallic counterparts. However, as small-sized NPs possess high surface energy, agglomeration during catalytic reactions is favored. Sufficient stabilization can be achieved by confinement of NPs in porous support materials. In this sense, metal–organic frameworks (MOFs) in particular have gained a lot of attention during the last years; however, encapsulation of bimetallic species remains challenging. Herein, the exclusive embedding of preformed core–shell PdPt and RuPt NPs into chemically robust Zr-based MOFs is presented. Microstructural characterization manifests partial retention of the core–shell systems after successful encapsulation without harming the crystallinity of the microporous support. The resulting chemically robust NP@UiO-66 materials exhibit enhanced catalytic activity towards the liquidphase hydrogenation of nitrobenzene, competitive with commercially used Pt on activated carbon, but with superior size-selectivity for sterically varied substrates.

DOI： 10.1002/chem.201603984

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© The Author 2016. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. Cs-corrected atomic resolution scanning transmission electron microscopy under a drift-compensated operation enabled us to acquire high-angle annular dark-field (HAADF) images of entire gold nanorods without distortion induced by specimen drift. The precision in locating the atomic columns was evaluated to be ± 5 pm in the images thus obtained,which is comparable to the image pixel size. A high-precision HAADF image of a single-crystalline gold nanorod revealed that the tip portions at both ends tended to undergo outward displacements along the rod axis and inward contraction along the perpendicular direction. A single nanosecond pulse shot of laser light with a wavelength of 1064 nm and an average intensity of 7.3 kJ/m2 pulse deformed the nanorods into spherical shapes. Simultaneously,the particle interior was completely changed into a multiple twin structure. Substantial displacements of atomic columns on the order of several tens of picometers were confirmed to be localized in the corners of domains at multiple twin junctions. Both the magnitude and direction of displacements were linearly relaxed with increasing distance from a multiple junction.

DOI： 10.1093/jmicro/dfw018

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© 2016 Elsevier Ltd Structure and accumulation behavior of ion tracks in CeO2 irradiated with 200 MeV Xe ions were examined by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) to obtain fundamental knowledge on the microstructure evolution induced by fission fragments in nuclear fuels and transmutation targets, which is of importance for the development of advanced fuel/target materials at high burn-up conditions. Bright-field (BF) TEM images of ion tracks from an inclined direction showed Fresnel contrast along penetrating path of incident ions. The signal intensity of high-angle annular dark-field (HAADF) STEM images was decreased at the core damage region of ion tracks along the path of ions, revealing the reduction of atomic density inside the ion track. Preferential formation of smaller and larger ion tracks was observed at a high ion fluence of 1 × 1014 cm−2 compared to a low ion fluence of 1 × 1011 cm−2. Results were discussed due to the coalescences and incomplete recovery of the core damage regions during the overlap of high density electronic excitation damage, which is induced during the repetition of the formation and recovery of ion tracks within an influence region.

DOI： 10.1016/j.pnucene.2016.07.013

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Rh is one of the most important noble metals for industrial applications. A major fraction of Rh is used as a catalyst for emission control in automotive catalytic converters because of its unparalleled activity toward NO x reduction. However, Rh is a rare and extremely expensive element; thus, the development of Rh alternative composed of abundant elements is desirable. Pd and Ru are located at the right and left of Rh in the periodic table, respectively, nevertheless this combination of elements is immiscible in the bulk state. Here, we report a Pd-Ru solid-solution-alloy nanoparticle (Pd x Ru 1-x NP) catalyst exhibiting better NO x reduction activity than Rh. Theoretical calculations show that the electronic structure of Pd 0.5 Ru 0.5 is similar to that of Rh, indicating that Pd 0.5 Ru 0.5 can be regarded as a pseudo-Rh. Pd 0.5 Ru 0.5 exhibits better activity than natural Rh, which implies promising applications not only for exhaust-gas cleaning but also for various chemical reactions.

DOI： 10.1038/srep28265

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Spatial configurations and lateral morphology of the 14H long-period stacking ordered (LPSO) phase have been studied by single tilt-axis electron tomography using high-voltage scanning transmission electron microscopy (STEM) operated at 1 MV. A "Quonset hut-like" lateral shape of the LPSO was found in a tomogram of a specimen as thick as 1.7 μ m. The reconstructed volume reveals spatial distribution of residual particulate precipitates of (Mg, Zn)₃Gd phase 20-30 nm in diameters. The precipitates act as a source of solute elements for the formation and growth processes of 14H LPSO. 1 MV-STEM realizes enough resolution for imaging the morphology of LPSO as well as high electron transmittance (∼4.1 μ m) without any obvious electron irradiation damages on microstructures.

DOI： 10.2320/matertrans.M2016021

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ammonia is a crucial chemical feedstock for fertilizer production and is a potential energy carrier. However, the current method of synthesizing ammonia, the Haber-Bosch process, consumes a great deal of energy. To reduce energy consumption, a process and a substance that can catalyze ammonia synthesis under mild conditions (low temperature and low pressure) are strongly needed. Here we show that Ru/Pr₂O₃ without any dopant catalyzes ammonia synthesis under mild conditions at 1.8 times the rates reported with other highly active catalysts. Scanning transmission electron micrograph observations and energy dispersive X-ray analyses revealed the formation of low-crystalline nano-layers of ruthenium on the surface of Pr₂O₃. Furthermore, CO₂ temperature-programmed desorption revealed that the catalyst was strongly basic. These unique structural and electronic characteristics are considered to synergistically accelerate the rate-determining step of NH₃ synthesis, cleavage of the N&z.tbd;N bond. We expect that the use of this catalyst will be a starting point for achieving efficient ammonia synthesis.

DOI： 10.1039/C6SC02382G

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This article anticipates the development of dual Lewis acidic/basic alloyed nanoparticle (NP) of poly(N-vinyl-2-pyrrolidone)-stabilized Pd0.5Ru0.5 solid solution, revealing equivalent Pdδ+ and Ruδ- on the NP surface. This unsupported NP disclosed excellent catalytic efficiency with high turnover frequency, 15 000 h-1 in Suzuki-Miyaura cross-coupling under notable drop of both Pd loading (0.08 mol %) and time (5 min) in air, attributed for its bifunctional acidic/basic modes. The bifunctional modes exposed the most interesting new reaction mechanism ascribed by the inductive effects of p-substituents in arylboronic acid, accelerated reactivity by electron-withdrawing group, revealing an opposite reactivity trend relative to other Pd-based catalysts. Besides, the significant drops of Pd loading and reaction time impeded the metal leaching associated with no changes in NP surface composition/structure after the 3rd cycle (>99 % efficiency), revealing a line-up for this NP in the environmental sustainability. Opposing charges, working together: Bifunctional Lewis acidic/basic Pdδ+Ruδ-(1:1) solid-solution nanoparticles disclose a remarkable catalytic efficiency in the Suzuki-Miyaura reaction at very low Pd loading and short reaction time in air. It reveals enhanced reactivity by the electron-withdrawing groups on arylboronic acids, resulting negatively charged aromatic ring in the transition state, which is a clear controversy to the conventional Pd catalysis.

DOI： 10.1002/cctc.201500758

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© The Royal Society of Chemistry 2015. We demonstrate a novel, simple synthetic method for metal (Ni) NPs in a MOF using the partial thermal decomposition of nickel(II) 2,5-dihydroxyterephthalate (Ni-MOF-74). The Ni NPs inside the Ni-MOF-74 are several nanometers in size, and the size can be precisely controlled by the heating conditions.

DOI： 10.1039/c5cc04663g

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© The Royal Society of Chemistry. We succeeded in the efficient preparation of well-dispersed Fe-Co nanoalloys (NAs) using the arc plasma deposition method. Synchronous shots of dual arc plasma guns were applied to a carbon support to prepare the solid-solution type Fe-Co NAs having an approximately 1 : 1 atomic ratio. The alloy structures with and without a reductive thermal treatment under a hydrogen atmosphere were examined using X-ray powder diffraction, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray analysis, high resolution STEM, and magnetic measurements, suggesting that highly crystalline spherical particles of ordered B2-type Fe-Co NAs form by the thermal treatment of the deposited grains.

DOI： 10.1039/c5dt02815a

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© the Owner Societies 2015. We demonstrate electric power generation via the electrooxidation of ethylene glycol (EG) on a series of Fe-group nanoalloy (NA) catalysts in alkaline media. A series of Fe-group binary NA catalysts supported on carbon (FeCo/C, FeNi/C, and CoNi/C) and monometallic analogues (Fe/C, Co/C, and Ni/C) were synthesized. Catalytic activities and product distributions on the prepared Fe-group NA catalysts in the EG electrooxidation were investigated by cyclic voltammetry and chronoamperometry, and compared with those of the previously reported FeCoNi/C, which clarified the contributory factors of the metal components for the EG electrooxidation activity, C<inf>2</inf> product selectivity, and catalyst durability. The Co-containing catalysts, such as Co/C, FeCo/C, and FeCoNi/C, exhibit relatively high catalytic activities for EG electrooxidation, whereas the catalytic performances of Ni-containing catalysts are relatively low. However, we found that the inclusion of Ni is a requisite for the prevention of rapid degradation due to surface modification of the catalyst. Notably, FeCoNi/C shows the highest selectivity for oxalic acid production without CO<inf>2</inf> generation at 0.4 V vs. the reversible hydrogen electrode (RHE), resulting from the synergetic contribution of all of the component elements. Finally, we performed power generation using the direct EG alkaline fuel cell in the presence of the Fe-group catalysts. The power density obtained on each catalyst directly reflected the catalytic performances elucidated in the electrochemical experiments for the corresponding catalyst. The catalytic roles and alloying effects disclosed herein provide information on the design of highly efficient electrocatalysts containing Fe-group metals. This journal is

DOI： 10.1039/c5cp00954e

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Hydrogen has the potential to power much of the modern world with only water as a by-product, but storing hydrogen safely and efficiently in solid form such as magnesium hydride remains a major obstacle. A significant challenge has been the difficulty of proving the hydriding/dehydriding mechanisms and, therefore, the mechanisms have long been the subject of debate. Here we use in situ ultra-high voltage transmission electron microscopy (TEM) to directly verify the mechanisms of the hydride decomposition of bulk MgH2 in Mg-Ni alloys. We find that the hydrogen release mechanism from bulk (2 μm) MgH2 particles is based on the growth of multiple pre-existing Mg crystallites within the MgH2 matrix, present due to the difficulty of fully transforming all Mg during a hydrogenation cycle whereas, in thin samples analogous to nano-powders, dehydriding occurs by a 'shrinking core' mechanism.

DOI： 10.1038/srep08450

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 local structure in Mg-Zn-Gd alloys on formation process of long period stacking ordered (LPSO) structure have been investigated by x-ray absorption fine structure (XAFS) method. Analyses of the x-ray absorption near edge structure (XANES) spectra have been shown that the local structures around Zn and Gd are changed during high temperature aging.

記述言語：その他   掲載種別：研究論文（学術雑誌）  

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. The zinc-imidazolate-based framework ZIF-8 was loaded with preformed surfactant-stabilized bimetallic Pd/Au nanoparticles and its corresponding monometallic counterparts Au and Pd by a controlled encapsulation process during the ZIF-8 crystal growth. The nanoparticle-loaded materials were characterized by powder X-ray diffraction (PXRD), FTIR spectroscopy, N2-sorption measurements, as well as by transmission electron microscopy (TEM). The ZIF-8 matrix material remained intact and the NP@ZIF-8 materials revealed the permanent porosity of Brunauer-Emmett-Teller (BET) surface areas above 1100 m2 g-1. The nanoparticles are exclusively found inside the volume of the nanocrystals and exhibit unchanged composition and size distribution as revealed by TEM investigations. Additionally, scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed the solid solution-type alloying of Pd and Au in the embedded Pd/Au nanoparticles. The materials were briefly evaluated in aqueous-phase aerobic alcohol oxidation to investigate the synergetic effects of alloyed Pd/Au nanoparticles and the microporous, hydrophobic matrix ZIF-8. The imidazolate-based framework ZIF-8 was loaded with catalytically active mono- and bimetallic nanoparticles (Au, Pd, Pd/Au) by a seed-and-growth concept. Characterization of the synthesized materials was carried out by powder X-ray diffraction, N2 sorption, and advanced transmission electron microscopy. The catalytic activity towards aerobic alcohol oxidations was studied.

DOI： 10.1002/ejic.201402409

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Presented here is the synthesis of an ordered bcc copper-palladium nanoalloy, via the decomposition of a Pd nanoparticle@metal-organic framework composite material. In situ XRD measurements were performed in order to understand the mechanism of the decomposition process. This result gives a further perspective into the synthesis of new nanomaterials via metal-organic framework decomposition. © 2014 Partner Organisations.

DOI： 10.1039/c4cc05941g

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： 10.1017/S1431927614004127

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H 2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5- benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating. © 2014 Macmillan Publishers Limited. All rights reserved.

DOI： 10.1038/nmat4030

記述言語：その他   掲載種別：研究論文（学術雑誌）  

An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO2 -free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO2, produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C 2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4 V vs. the reversible hydrogen electrode (RHE), without CO2 generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system.

DOI： 10.1038/srep05620

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Pd octahedrons and cubes enclosed by {111} and {100} facets, respectively, have been synthesized for investigation of the shape effect on hydrogen-absorption properties. Hydrogen-storage properties were investigated using in situ powder X-ray diffraction, in situ solid-state 2H NMR and hydrogen pressure-composition isotherm measurements. With these measurements, it was found that the exposed facets do not affect hydrogen-storage capacity; however, they significantly affect the absorption speed, with octahedral nanocrystals showing the faster response. The heat of adsorption of hydrogen and the hydrogen diffusion pathway were suggested to be dominant factors for hydrogen-absorption speed. Furthermore, in situ solid-state 2H NMR detected for the first time the state of 2H in a solid-solution (Pd + H) phase of Pd nanocrystals at rt. © 2014 American Chemical Society.

DOI： 10.1021/ja504699u

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We have investigated atomic structure of ion tracks in CeO2 irradiated with 200 MeV Xe ions by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). TEM observations under inclined conditions showed continuous ion tracks with diffraction and structure factor contrast, and the decrease in the atomic density of the ion tracks was evaluated to be about 10%. High resolution STEM with high-angle annular dark-field (HAADF) technique showed that the crystal structure of the Ce cation column is retained at the core region of ion tracks, although the signal intensity of the Ce cation lattice is reduced over a region 4-5 nm in size. Annular bright field (ABF) STEM observation has detected that the O anion column is preferentially distorted at the core region of ion tracks within a diameter of 4 nm. The core region of ion track in CeO2 is determined to contain a high concentration of vacancies or small vacancy clusters and to generate interstitials in surrounding regions. © 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2013.10.077

記述言語：その他   掲載種別：研究論文（学術雑誌）  

PdxRu1-x solid solution alloy nanoparticles were successfully synthesized over the whole composition range through a chemical reduction method, although Ru and Pd are immiscible at the atomic level in the bulk state. From the XRD measurement, it was found that the dominant structure of PdxRu1-x changes from fcc to hcp with increasing Ru content. The structures of PdxRu1-x nanoparticles in the Pd composition range of 30-70% consisted of both solid solution fcc and hcp structures, and both phases coexist in a single particle. In addition, the reaction of hydrogen with the PdxRu1-x nanoparticles changed from exothermic to endothermic as the Ru content increased. Furthermore, the prepared PdxRu1-x nanoparticles demonstrated enhanced CO-oxidizing catalytic activity; Pd0.5Ru0.5 nanoparticles exhibit the highest catalytic activity. This activity is much higher than that of the practically used CO-oxidizing catalyst Ru and that of the neighboring Rh, between Ru and Pd. © 2014 American Chemical Society.

DOI： 10.1021/ja409464g

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A pulsed laser light illumination system was attached to a high-voltage electron microscope (HVEM) for in situ observation of light-induced behaviors of nano objects. The wavelength λ of emitted laser pulses was 1064, 532 or 266 nm, and the pulse duration was 6-8 ns. Using this combined HVEM system, we observed the deformation behavior of gold nanorods irradiated by a pulsed laser (λ = 1064 nm) at an intensity of 310 J m^-2 pulse or higher. A single shot of pulsed laser reduced the aspect ratio of the gold nanorods from 5 to a much smaller value. The extent of the reduction increased at higher laser intensities. However, at 310 J m^-2 pulse^-1, additional pulsed shots induced limited further deformation. The mean aspect ratio approximated to 2.5 even after irradiation with 7 pulses (total fluence exceeding 2 MJ m^-2). In situ high resolution transmission electron microscopy (HRTEM) observation revealed that deformation was accompanied by total atomic restructuring of the nanorod interiors.

DOI： 10.1093/jmicro/dfu012

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 have investigated the atomistic structure of radiation-induced defects in CeCO2 formed under 200 keV electron irradiation. Dislocation loops on {111} habit planes are observed, and they grow accompanying strong strain-field. Atomic resolution scanning transmission electron microscopy (STEM) observations with high angle annular dark-field (HAADF) and annular bright-field (ABF) imaging techniques showed that no additional Ce layers are inserted at the position of the dislocation loop, and that strong distortion and expansion is induced around the dislocation loops. These results are discussed that dislocation loops formed under electron irradiation are non-stoichiometric defects consist of oxygen interstitials.

DOI： 10.1557/opl.2013.199

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The addition of 200. ppm strontium to an Al-10. wt% Si casting alloy changes the morphology of the eutectic silicon phase from coarse plate-like to fine fibrous networks. In order to clarify this modification mechanism the location of Sr within the eutectic Si phase has been investigated by a combination of high-resolution methods. Whereas three-dimensional atom probe tomography allows us to visualise the distribution of Sr on the atomic scale and to analyse its local enrichment, transmission electron microscopy yields information about the crystallographic nature of segregated regions. Segregations with two kinds of morphologies were found at the intersections of Si twin lamellae: Sr-Al-Si co-segregations of rod-like morphology and Al-rich regions of spherical morphology. Both are responsible for the formation of a high density of multiple twins and promote the anisotropic growth of the eutectic Si phase in specific crystallographic directions during solidification. The experimental findings are related to the previously postulated mechanism of "impurity induced twinning". © 2012.

DOI： 10.1016/j.ultramic.2012.10.006

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated microstructure evolution in CeO₂ irradiated with 210 MeV Xe ions by using transmission electron microscopy to gain the fundamental knowledge on radiation damage induced by fission fragments in nuclear fuel and transmutation target. Analysis on the accumulation of ion tracks has revealed an influence region to recover pre-existing core damage regions of ion tracks to be 8.4 nm in radius. Cross section observations showed that high-density electronic excitation induces both ion tracks and dislocation loops. At high fluences of 1.5 × 10¹⁹ and 1 × 10 ²⁰ ions m^-2, depth-dependent microstructure was developed with radiation-induced defects of ion tracks, dislocation loops (dot-contrast) and line dislocations. Formation of sub-divided small grains was found at shallow depth at a fluence of 1 × 10²⁰ ions m^-2. The microstructure evolution was discussed in terms of the accumulation of interstitials due to significant overlap of high density electronic excitation.

DOI： 10.1016/j.nimb.2013.04.069

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the first discovery of pure face-centered-cubic (fcc) Ru nanoparticles. Although the fcc structure does not exist in the bulk Ru phase diagram, fcc Ru was obtained at room temperature because of the nanosize effect. We succeeded in separately synthesizing uniformly sized nanoparticles of both fcc and hcp Ru having diameters of 2-5.5 nm by simple chemical reduction methods with different metal precursors. The prepared fcc and hcp nanoparticles were both supported on γ-Al₂O₃, and their catalytic activities in CO oxidation were investigated and found to depend on their structure and size.

DOI： 10.1021/ja311261s

記述言語：その他   掲載種別：研究論文（学術雑誌）  

We report the first discovery of pure face-centered-cubic (fcc) Ru nanoparticles. Although the fcc structure does not exist in the bulk Ru phase diagram, fcc Ru was obtained at room temperature because of the nanosize effect. We succeeded in separately synthesizing uniformly sized nanoparticles of both fcc and hcp Ru having diameters of 2-5.5 nm by simple chemical reduction methods with different metal precursors. The prepared fcc and hcp nanoparticles were both supported on γ-Al2O3, and their catalytic activities in CO oxidation were investigated and found to depend on their structure and size. © 2013 American Chemical Society.

DOI： 10.1021/ja311261s

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 have investigated the structure of ion tracks in magnesium aluminate spinel (MgAl₂O₄) and ceria (CeO₂) irradiated with 200 MeV Xe ions. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) techniques have shown that ion tracks in both materials retain crystallinity. The atomic density inside the core damage region of ion tracks is decreased to generate interstitial atoms at the peripheral region. Overlap of high-density electronic excitation at high fluence has revealed the development of dislocation structure in both MgAl ₂O₄ and ceria CeO₂: the preferential occupation of cations in tetrahedral sites was found in MgAl₂O₄, and the formation of small sub-grains was observed in CeO₂.

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The intermetallic compound Cu 6Sn 5 is a significant microstructural feature of many electronic devices where it is present at the solder-substrate interfaces. The time- and temperature-dependent thermomechanical properties of Cu 6Sn 5 are dependent on the nature and stability of its crystal structure, which has been shown to exist in at least four variants (η, η', η 6 and η 8). This research details an additional newly identified monoclinic-based structure in directly alloyed stoichiometric Cu 6Sn 5 using variable-temperature synchrotron X-ray diffraction (XRD) and transmission electron microscopy. The phase is associated with a departure from the equilibrium temperature of the polymorphic monoclinic-hexagonal transformation temperature. The new monoclinic phase can be treated as a modulation of four η 8-Cu 5Sn 4 unit cells plus one η'-Cu 6Sn 5 unit cell. It has been labeled as η 4+1 and has cell parameters of a = 92.241 Å, b = 7.311 Å, c = 9.880 Å and β = 118.95° determined from electron diffraction patterns. The XRD results could be fitted well to a Rietveld refinement using the new crystal parameters. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2012.08.024

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Small amounts of strontium can transform the morphology of the eutectic silicon phase present in Al-Si casting alloys from coarse plate-like to fine fibrous networks. In order to understand this industrially important but hitherto insufficiently understood effect, the strontium distribution was studied in atomic resolution by atom probe tomography and in nanometre resolution by transmission electron microscopy. The combined investigations indicate that Sr co-segregates with Al and Si within the eutectic Si phase. Two types of segregations were found: (i) nanometre-thin rod-like co-segregations of type I are responsible for the formation of multiple twins in a Si crystal and enable its growth in different crystallographic directions; (ii) type II segregations come as more extended structures, restrict growth of a Si crystal and control its branching. We show how Sr enables both kinds of mechanisms previously postulated in the literature, namely "impurity-induced twinning" (via type I) and growth restriction of eutectic Si phase (via type II). © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2012.03.031

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Accumulation and recovery of radiation-induced damage with swift heavy ions in stoichiometric magnesium aluminate spinel, MgAl2O4, has been investigated. Microstructural change and atomic disordering was examined through transmission electron microscopy (TEM) techniques, with bright-field (BF) and high-resolution (HR) TEM images, and high angular resolution electron channelling X-ray spectroscopy (HARECXS), for single crystal MgAl2O4 irradiated with 200 MeV Xe, and 340 or 350 MeV Au ions. The density of core damage region, detected by BFTEM with Fresnel-contrast, increased proportionally with ion fluence at the early stage of accumulation and saturated at a fluence higher than 10(16) ions m(-2). This result is discussed with a balance between the formation and recovery of the core damage region under irradiation, and the influence region to induce the recovery was evaluated to be 7-9 nm in radius. HARECXS and electron diffraction analysis revealed that cations at tetrahedral sites preferentially occupy octahedral sites to transform to defective rock-salt structure. The structure of the core damage region is found from HR and BFTEM images to be a columnar vacancy-rich region with a low atomic density.

DOI： 10.3139/146.110564

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）  

Molecular dynamics simulations of oxygen Frenkel pairs (FPs) in cerium dioxide (CeO2) were carried out in order to understand their kinetic behavior. The results show that an oxygen FP recombine with the vacancy and the interstitial after the vacancy jump preferentially along the 〈1 0 0〉 direction. When multiple oxygen FPs are introduced, the interstitials aggregate into a (1 1 1) plate-like cluster at relatively lower temperature lower than 600 K, while they recombine with vacancies at elevated temperatures higher than 900 K within 10 ps. Molecular mechanics calculations of oxygen FPs on a (1 1 1) plane show that the formation energy per a FP decreases with increase of the number of FPs. The theoretical results are consistent with the transmission electron microscopy observations of formation of 1/9〈1 1 1〉{1 1 1} oxygen interstitial platelets in CeO2 under electron irradiation. © 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2010.05.022

記述言語：その他   掲載種別：研究論文（学術雑誌）  

The epitaxial and homogeneous irradiation induced re-crystallization of amorphous MgAl2O4 was studied by means of continuous Frenkel pair accumulation in the molecular dynamics framework. Present results point out that the re-crystallization induced by Frenkel pair accumulation appears in both cases to be thermally enhanced but non diffusive. It is governed by a local rearrangement of each point defect in the homogeneous case, while spontaneous Frenkel pair recombination process in the crystalline part or at the interface drives the re-crystallization in the epitaxial case. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2008.06.027

記述言語：その他   掲載種別：研究論文（学術雑誌）  

This paper investigates the formation process of radiation-induced defects in magnesium aluminate spinel and their stability using transmission electron microscopy, with emphasis on the effects of electronic excitation. Small interstitial-type dislocation loops disappeared under electron-induced electronic excitation. The elimination rate of the loops was found to be one order higher than for α-alumina. The disappearance of dislocation loops by a dissociation mechanism into isolated interstitials is discussed through analysis of the growth-and-shrink process of the loops. HARECXS analysis on cross section specimens irradiated with 350 MeV Au ions has shown the progress of cation disordering along ion tracks to be a function of electronic stopping power, (dE/dx)e. Cations were found to exchange their sites toward a random configuration. Such disordering appears from (dE/dx)e = 10 keV/nm, and increases in size with increasing (dE/dx)e to reach nearly 10 nm in diameter at 30 keV/nm, under an assumption of a fully disordered configuration. © 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2008.03.127

記述言語：英語   掲載種別：研究論文（その他学術会議資料等）  

Molecular dynamics (MD) simulations of oxygen Frenkel pairs (FPs) in cerium dioxide (CeO₂) were carried out in order to understand their kinetic behavior. The results show that an oxygen FP annihilates by recombination of the vacancy and the interstitial after the vacancy jump along the <100> direction. When multiple oxygen FPs are introduced, the interstitials aggregate into a (111) plate-like cluster at relatively lower temperature, while they annihilate by recombination with vacancies at elevated temperatures. The theoretical results are consistent with the transmission electron microscopy (TEM) observations of formation of {111} oxygen interstitial platelets in CeO₂ under electron irradiation.

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 kinetic of phase transitions under irradiation of MgAl₂O₄ has been studied using molecular dynamics (MD) simulation by means of continuous cation Frenkel pair (FP) accumulation. Three different cases have been considered: cation FP accumulation starting (i) from the normal (N) spinel, (ii) from the amorphous (A) spinel and (iii) from the interface between rock-salt (NaCl) spinel and A-spinel. When submitted to FP accumulation, the N-spinel transits directly towards the NaCl-spinel for temperature lower than 600K. For temperatures higher than 600K, the dose needed to obtain the rock-salt structure increases with temperature, and the structure transits to an intermediate disordered (D) structure prior to the NaCl-spinel. No amorphization of the spinel under FP accumulation is obtained for doses up to 68 displacements per cation at 30K. The dose - temperature dependence relies on thermally activated FP recombination processes. The epitaxial and homogeneous irradiation induced re-crystallization of amorphous MgAl₂O₄ was obtained by continuous FP accumulation. Present results point out that the re-crystallization induced by FP accumulation appears in both cases to be thermally enhanced but non diffusive. It is governed by a local rearrangement of each point defect in the homogeneous case, while spontaneous FP recombination process in the crystalline part or at the interface drives the recrystallization in the epitaxial case. In summary, the thermally enhanced - but non diffusive - Frenkel pair recombination or local relaxation of point defects may play a central role to the radiation resistance of MgAl₂O₄.

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Atomic resolution transmission-electron microscopy (TEM) observations and analysis have been undertaken on magnesium aluminate spinel to understand the structure of ion tracks induced by swift heavy ions. A combination of TEM techniques, which includes high-resolution and bright-field (BF) imaging, and high angular resolution electron channeling spectroscopy (HARECXS) analysis, disclosed the atomic structure of ion tracks. Swift heavy ions induce cation disordering along the latent tracks for a widespread region of 10 nm in diameter, which is much larger than a strained region detected by BF diffraction contrast. A preferential migration of cations is induced from the tetrahedral to octahedral interstitial site at the core regions of ion tracks under a condition of higher electronic excitation of (dE/dx)e = 35 keV/nm.

DOI： 10.1007/s11837-007-0050-3

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Microstructure change and atomic disordering in MgO · nAl2O3 (n = 1.1) irradiated with 350 MeV Au ions (Se = 35 keV/nm) were investigated through transmission electron microscopy (TEM) and high angular resolution electron channeling X-ray spectroscopy (HARECXS) techniques. High resolution TEM revealed that each ion track maintains crystalline structure. The core region of ion track is found to reveal a lattice fringe with a half period of spinel matrix, suggesting the phase transformation from spinel to rock-salt structure. HARECXS analysis clearly showed progress of cation disorder at a significantly large region of ∼10 nm in diameter. These results are compared with the previous results of 200 MeV Xe ion irradiated spinel (Se = 25 keV/nm). The structure of ion tracks is found to consist of three concentric circle structures: the defective core region (∼2 nm in diameter), strained region (∼5 nm) and cation disordered region (10-12 nm). © 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2006.04.164

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）  

We have investigated the microstructure and atomic disordering of nearly stoichiometric magnesium aluminate spinel (MgO • 1.1Al2O 3), irradiated with 200 MeV Xe14+ ions (Se = 25 keV/nm). Transmission electron microscopy techniques of bright-field (BF) and high-resolution (HR) imaging, as well as high angular resolution electron channeling X-ray spectroscopy (HARECXS) were employed for quantitative analysis of radiation-induced structural change. BF images of ion tracks show columnar dark contrast of ∼4 nm in diameter accompanying distinct black or white dots at the incident surface. Clear lattice fringes are observed in HR images even inside the ion tracks, indicating that the spinel crystals are not amorphized but partially disordered along the ion tracks. HARECXS analysis showed that cation disordering progresses successively with ion fluence, and the disordered regions are found to extend over 12.8 ± 0.9 nm in diameter for Al ions and 9.6 ± 0.6 nm for Mg ions along the ion tracks. This chemically disordered region is much larger than the strained volume detected by BF and HR images. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nimb.2005.11.108

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）  

Radiation-induced defects in α-alumina were investigated through transmission electron microscopy for specimens irradiated with 100 keV He + ions at 760 K with an electric field of 100 kV/m. Ion-irradiation with an electric field induces characteristic defect clusters, such as bundles of long-shaped defect clusters, aluminum colloid and γ-alumina precipitates, and interstitial type-dislocation loops, though only dislocation loops were formed when the material is irradiated without an electric field. Electron microscopy analysis has revealed the lattice displacement vector of long-shaped defects, and the crystallographic relationship among α-alumina matrix, aluminum colloid and γ-alumina. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnucmat.2004.04.160

開催年月日： 2023年6月

記述言語：日本語   会議種別：口頭発表（一般）  

国名：日本国  

開催年月日： 2023年3月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：東京大学　駒場キャンパス   国名：日本国  

開催年月日： 2022年10月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：JA長野県ビル   国名：日本国  

開催年月日： 2022年10月

記述言語：日本語   会議種別：口頭発表（一般）  

開催地：早稲田大学 西早稲田キャンパス   国名：日本国  

開催年月日： 2022年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Big Palette Fukushima   国名：日本国