| Yoshihiro Yamazaki | Last modified date：2023.11.27 |
Professor /
Kyushu University Platform of Inter/Transdisciplinary Energy Research
Papers
| 1. | K. Hoshino†, S. Kasamatsu†, J. Hyodo, K. Yamamoto, H. Setoyama, T. Okajima, Y. Yamazaki, Probing Local Environments of Oxygen Vacancies Responsible for Hydration in Sc-Doped Barium Zirconates at Elevated Temperatures: In Situ X-ray Absorption Spectroscopy, Thermogravimetry, and Active Learning Ab Initio Replica Exchange Monte Carlo Simulations, Chemistry of Materials, https://doi.org/10.1021/acs.chemmater.2c02116, 35, 2289-2301, 2023.03. |
| 2. | Junji Hyodo , Yoshihiro Yamazaki, Quantitative evaluation of biaxial compressive strain and its impact on proton conduction and diffusion in yttrium-doped barium zirconate epitaxial thin films, Journal of Physics: Energy, 10.1088/2515-7655/ac889e, 4, 1-16, 2022.09, [URL], Proton-conducting oxides, including 20 mol% yttrium-doped BaZrO3 (BZY20), have attracted considerable attention as electrolytes for environmentally friendly electrochemical cells, such as proton ceramic fuel cells (PCFCs) and proton-conducting solid oxide cells. These oxides exhibit fast proton conduction due to the complex physicochemical phenomena of hydration, chemical lattice expansion, proton migration, proton trapping, and local distortion. Using a proton-conducting oxide as an electrolyte film in electrochemical devices introduces an interface, which thermally and chemically generates mechanical strain. Here, we briefly review the current state of research into proton-conducting oxides in bulk samples and films used in electrochemical devices. We fabricated 18 and 500 nm thick 20 mol% BZY20 epitaxial films on (001) Nb-doped SrTiO3 single-crystal substrates to form a model interface between proton-conductive and non-proton-conductive materials, using pulsed laser deposition, and quantified the mechanical strain, proton concentration, proton conductivity, and diffusivity using thin-film x-ray diffractometry, thermogravimetry, secondary ion mass spectrometry, and AC impedance spectroscopy. Compressive strains of −2.1% and −0.85% were measured for the 18 and 500 nm thick films, respectively, and these strains reduced both the proton conduction and diffusion by five and one orders of magnitude, respectively, at 375 °C. Analysis based on a simple trapping model revealed that the decrease in proton conduction results from the slower diffusion of mobile protons with a negligible change in the proton trapping contribution. The model shows that the high ohmic resistance reported for a high-performance PCFC with a power density of 740 mW cm−2 at 600 °C can be solely explained by the estimated compressive strain in the cells. This study shows that minimizing biaxial compressive strain by appropriate choices of the electrolyte–electrode combination and fabrication process is important for maximizing the performance of electrochemical cells.. |
| 3. | J. Hyodo, K. Tsujikawa, M. Shiga, Y. Okuyama, Y. Yamazaki, Accelerated Discovery of Proton-Conducting Perovskite Oxide by Capturing Physicochemical Fundamentals of Hydration, ACS Energy Letters, 10.1021/acsenergylett.1c0 1239, 6, 2985-2992, 2021.08. |
| 4. | Junji Hyodo, Koki Kitabayashi, Kenta Hoshino, Yuji Okuyama, Yoshihiro Yamazaki, Fast and Stable Proton Conduction in Heavily Scandium-Doped Polycrystalline Barium Zirconate at Intermediate Temperatures, Advanced Energy Materials, 10.1002/aenm.202000213, 10, 25, 2000213, 2020.07, The environmental benefits of fuel cells and electrolyzers have become increasingly recognized in recent years. Fuel cells and electrolyzers that can operate at intermediate temperatures (300–450 °C) require, in principle, neither the precious metal catalysts that are typically used in polymer-electrolyte-membrane systems nor the costly heat-resistant alloys used in balance-of-plant components of high-temperature solid oxide electrochemical cells. These devices require an electrolyte with high ionic conductivity, typically more than 0.01 S/cm, and high chemical stability. To date, however, high ionic conductivities have been found in chemically unstable materials such as CsH2PO4, In-doped SnP2O7, BaH2, and LaH3−2Ox. Here, fast and stable proton conduction in 60-at% Sc-doped barium zirconate polycrystal, with a total conductivity of 0.01 S cm−1 at 396 °C for 200 h is demonstrated. Heavy doping of Sc in barium zirconate simultaneously enhances the proton concentration, bulk proton diffusivity, specific grain boundary conductivity, and grain growth. An accelerated stability test under a highly concentrated and humidified CO2 stream using in situ X-ray diffraction shows that the perovskite phase is stable over 240 h at 400 °C under 0.98 atm of CO2. These results show great promises as an electrolyte in solid-state electrochemical devices operated at intermediate temperatures.. |
| 5. | Y. Yamazaki, A. Kuwabara, J. Hyodo, Y. Okuyama, C.A.J. Fisher, S.M. Haile, Oxygen affinity: the missing link enabling prediction of proton conductivities in doped barium zirconates, Chemistry of Materials, https://doi.org/10.1021/acs.chemmater.0c01869, 32, 17, 7292-7300, 2020.09, Proton-conducting oxides, specifically doped barium zirconates, have garnered much attention as electrolytes for solid-state electrochemical devices operable at intermediate temperatures (400− 600 °C). In chemical terms, hydration energy, Ehyd, and proton− dopant association energy, Eas, are two key parameters that determine whether an oxide exhibits fast proton conduction, but to date ab initio studies have for the most part studied each parameter separately, with no clear correlation with proton conductivity identified in either case. Here, we demonstrate that the oxygen affinity, EO.dopant, defined as the energy released when an oxide ion enters an oxygen vacancy close to a dopant atom, is the missing link between these two parameters and correlates well with experimental proton conductivities in doped barium zirconates. Ab initio calculations of point defects and their complexes in Sc-, In-, Lu-, Er-, Y-, Gd-, and Eu-doped barium zirconates are used to determine Ehyd, Eas, EO.dopant, and the hydrogen affinity, EH.host, of each system. These four energy terms are related by Ehyd = EO.dopant + 2EH.host + 2Eas. Complementary impedance spectroscopy measurements reveal that the stronger the calculated oxygen affinity of a system, the higher the proton conductivity at 350 °C. Although the proton trapping site is also an important factor, the results show that oxygen affinity is an excellent predictor of proton conductivity in these materials.. |
| 6. | Shunta Nishioka, Junji Hyodo, Junie Jhon M. Vequizo, Shunsuke Yamashita, Hiromu Kumagai, Koji Kimoto, Akira Yamakata, Yoshihiro Yamazaki, Kazuhiko Maeda, Homogeneous Electron Doping into Nonstoichiometric Strontium Titanate Improves Its Photocatalytic Activity for Hydrogen and Oxygen Evolution, ACS Catalysis, 10.1021/acscatal.8b01379, 8, 8, 7190-7200, 2018.08, Water splitting using a semiconductor photocatalyst has been extensively studied as a means of solar-to-hydrogen energy conversion. Powder-based semiconductor photocatalysts, in particular, have tremendous potential in cost mitigation due to system simplicity and scalability. The control and implementation of powder-based photocatalysts are, in reality, quite complex. The identification of the semiconductor-photocatalytic activity relationship and its limiting factor has not been fully solved in any powder-based semiconductor photocatalyst. In this work, we present systematic and quantitative evaluation of photocatalytic hydrogen and oxygen evolution using a model strontium titanate powder/aqueous solution interface in a half reaction. The electron density was controlled from 1016 to 1020 cm-3 throughout the strontium titanate powder by charge compensation with oxygen nonstoichiometry (the amount of oxygen vacancy) while maintaining its crystallinity, chemical composition, powder morphology, and the crystal and electronic structure of the surface. The photocatalytic activity of hydrogen evolution from aqueous methanol solution was stable and enhanced by 40-fold by the electron doping. The enhancement was correlated well with increased Δabsorbance, an indication of prolonged lifetime of photoexcited electrons, observed by transient absorption spectroscopy. Photocatalytic activity of oxygen evolution from aqueous silver nitrate solution was also enhanced by 3-fold by the electron doping. Linear correlation was found between the photocatalytic activity and the degree of surface band bending, ΔΦ, above 1.38 V. The band bending, potential downhill for electronic holes, enlarges the total flux of photoexcited holes toward the surface, which drives the oxygen evolution reaction.. |
| 7. | Junie Jhon M. Vequizo, Shunta Nishioka, Junji Hyodo, Yoshihiro Yamazaki, Kazuhiko Maeda, Akira Yamakata, Crucial impact of reduction on the photocarrier dynamics of SrTiO3 powders studied by transient absorption spectroscopy, Journal of Materials Chemistry A, 10.1039/c9ta08216f, 7, 45, 26139-26146, 2019.01, Inducing oxygen vacancy defects in SrTiO3 powders via high temperature treatment in the presence of a mixture of Ar, O2, dry air, and H2 ambient gases is a promising strategy to produce homogeneously defective SrTiO3 photocatalysts with a remarkable 40-fold enhancement of H2 evolution activity. Electron doping of SrTiO3 due to oxygen vacancies triggers the development of a highly active SrTiO3 photocatalyst; however, the photodynamic processes involved in these modifications of SrTiO3 have not been fully elucidated yet. In this work, we investigated the impact of high temperature treatment based on the dynamics of photocarriers by transient absorption spectroscopy (TAS). TAS results revealed that upon band gap excitation of SrTiO3, most of the photoexcited electrons in non-reduced SrTiO3 are deeply trapped in the intrinsic defects as evident from the strong broad absorption signals peaking at 11 000 cm-1 (909 nm, 1.36 eV) and 20 000 cm-1 (500 nm, 2.48 eV), whereas the absorption intensities in this wavenumber region largely decreased in highly reduced SrTiO3, suggesting a possible electron filling of deeply trapped states via reduction treatment (or electron doping). Interestingly, the photoexcited electrons in oxygen-deficient SrTiO3 preferably occupy the shallower electron traps. The lowest energy limit of the electron trap filled by photoexcited electrons is estimated to be at the absorption edge located at 1000 cm-1 (∼0.12 eV below the conduction band), which is much shallower than that of non-reduced SrTiO3 (>0.7 eV). Furthermore, it was found that the electron population in the shallow traps in highly reduced SrTiO3 is nearly 2 orders of magnitude higher compared to that in non-reduced SrTiO3, indicating a large improvement in the electron lifetime. The findings herein offer significant insights into the crucial impact of the reduction of SrTiO3via induced oxygen vacancy defects to provide available photoexcited electrons that can be readily utilized for the H2 generation reaction.. |
| 8. | Kenta Hoshino, Junji Hyodo, and Yoshihiro Yamazaki, Non-linear Behavior for Chemical Expansion in Yttrium-doped Barium Zirconate upon Hydration, Chemistry Letters, https://doi.org/10.1246/cl.200942, 50, 899-902, 2021.04. |
| 9. | Y. Uchiyama, J. Hyodo, Y. Yamazaki, Water Vapor Reduces the Effect of Cl-Poisoning on CO Oxidation over Pt/CeO2 Heterogeneous Catalysts, Chemistry Letters, https://doi.org/10.1246/cl.200835, 50, 888-891, 2021.04. |
| 10. | Yoshaiki Iijima, Yoshihiro Yamazaki, Interdiffusion between metals of widely different self-diffusion rates, Defect and Diffusion Forum, 10.4028/www.scientific.net/ddf.237-240.62, 237-240, PART 1, 62-73, 2005.04, Interdiffusion between metals of widely different diffusional characteristic is interesting in view of the fact that several anomalous features appear during interdiffusion owing to the large difference between the fluxes of the diffusing species. In some binary systems, it has been observed that the interdiffusion coefficients determined by multi-phase couples are smaller than those determined through the single-phase couples. This observation implies that the Boltzmann-Matano analysis is unapplicable to such cases. In the present article, this phenomenon is reviewed in the Au-Fe and Au-Ni systems, which have large differences in the diffusivities between the components. Recent experimental results on diffusion enhanced by vacancies induced under elevated hydrogen pressure are helpful to resolve the problems.. |
| 11. | Osamu Taguchi, Miyuki Hagiwara, Yoshihiro Yamazaki, Yoshiaki Iijima, Impurity diffusion of Al and Cu in y-Fe, Defect and Diffusion Forum, 10.4028/www.scientific.net/ddf.194-199.91, 194-199 PART 1, 91-96, 2001.04, Impurity diffusion of Al and Cu in γ-Fe has been studied by using non-radioactive tracer elements. Penetration profiles have been determined by the lathe sectioning and the instrumental analyses, namely, absorptiometry for Al and atomic absorption analysis for Cu. Penetration curves obtained have been good for the diffusion analysis. The absorptiometry and atomic absorption analysis are found to be useful to measure the penetration profile for the impurity diffusion in metals where suitable radioisotope as a tracer is unavailable or the half-life of radioisotope is very short.. |
| 12. | Yoshihiro Yamazaki, Peter Babilo, Sossina M. Haile, Defect chemistry of yttrium-doped barium zirconate A thermodynamic analysis of water uptake, Chemistry of Materials, 10.1021/cm800843s, 20, 20, 6352-6357, 2008.10, Thermogravimetry has been used to evaluate the equilibrium constants of the water incorporation reaction in yttrium-doped BaZrO3 with 20-40% yttrium in the temperature range 50-1000°C under a water partial pressure of 0.023 atm. The constants, calculated under the assumption of a negligible hole concentration, were found to be linear in the Arrhenius representation only at low temperatures (≤500 °C). Nonlinearity at high temperatures is attributed to the occurrence of electronic defects. The hydration enthalpies determined here range from -22 to -26 kJ mol-1 and are substantially smaller in magnitude than those reported previously. The difference is a direct result of the different temperature ranges employed, where previous studies have utilized higher temperature thermogravimetric measurements, despite the inapplicability of the assumption of a negligible hole concentration. The hydration entropies measured in this work, around -40 J K-1 mol -1, are similarly smaller in magnitude than those previously reported and are considerably smaller than what would be expected from the complete loss of entropy of vapor-phase H2O upon dissolution. This result suggests that substantial entropy is introduced into the oxide as a consequence of the hydration. The hydration reaction constants are largely independent of yttrium concentration, in agreement with earlier reports.. |
| 13. | Yoshihiro Yamazaki, Raul Hernandez-Sanchez, Sossina M. Haile, High total proton conductivity in large-grained yttrium-doped barium zirconate, Chemistry of Materials, 10.1021/cm900208w, 21, 13, 2755-2762, 2009.07, Barium zirconate has attracted particular attention among candidate proton conducting electrolyte materials for fuel cells and other electrochemical applications because of its chemical stability, mechanical robustness, and high bulk proton conductivity. Development of electrochemical devices based on this material, however, has been hampered by the high resistance of grain boundaries, and, due to limited grain growth during sintering, the high number density of such boundaries. Here, we demonstrate a fabrication protocol based on the sol - gel synthesis of nanocrystalline precursor materials and reactive sintering that results in large-grained, polycrystalline BaZr 0.8Y 0.2C 3-δ of total high conductivity, ∼ 1 × 10 -2 Scm -1 at 450 °C. The detrimental role of grain boundaries in these materials is confirmed via a comparison of the conductivities of polycrystalline samples with different grain sizes. Specifically, two samples with grain sizes differing by a factor of 2.3 display essentially identical grain interior conductivities, whereas the total grain boundary conductivities differ by a factor of 2.5-3.2, depending on the temperature (with the larger-grained material displaying higher conductivity).. |
| 14. | Yoshihiro Yamazaki, Raul Hernandez-Sanchez, Sossina M. Haile, Cation non-stoichiometry in yttrium-doped barium zirconate: phase behavior, microstructure and proton conductivity, Journal of Materials Chemistry, 20, 8158-8166, 2010.08. |
| 15. | Yoshihiro Yamazaki, Frédéric Blanc, Yuji Okuyama, Lucienne Buannic, Juan C. Lucio-Vega, Clare P. Grey, Sossina M. Haile, Proton trapping in yttrium-doped barium zirconate, Nature Materials, 10.1038/nmat3638, 12, 7, 647-651, 2013.07, The environmental benefits of fuel cells have been increasingly appreciated in recent years. Among candidate electrolytes for solid-oxide fuel cells, yttrium-doped barium zirconate has garnered attention because of its high proton conductivity, particularly in the intermediate-temperature region targeted for cost-effective solid-oxide fuel cell operation, and its excellent chemical stability. However, fundamental questions surrounding the defect chemistry and macroscopic proton transport mechanism of this material remain, especially in regard to the possible role of proton trapping. Here we show, through a combined thermogravimetric and a.c. impedance study, that macroscopic proton transport in yttrium-doped barium zirconate is limited by proton-dopant association (proton trapping). Protons must overcome the association energy, 29 kJ mol -1, as well as the general activation energy, 16 kJ mol -1, to achieve long-range transport. Proton nuclear magnetic resonance studies show the presence of two types of proton environment above room temperature, reflecting differences in proton-dopant configurations. This insight motivates efforts to identify suitable alternative dopants with reduced association energies as a route to higher conductivities.. |
| 16. | Chih Kai Yang, Yoshihiro Yamazaki, Aykut Aydin, Sossina M. Haile, Thermodynamic and kinetic assessments of strontium-doped lanthanum manganite perovskites for two-step thermochemical water splitting, Journal of Materials Chemistry A, 10.1039/c4ta02694b, 2, 33, 13612-13623, 2014.09, Solar-driven thermochemical water splitting using non-stoichiometric oxides has emerged as an attractive technology for solar fuel production. The most widely considered oxide for this purpose is ceria, but the extreme temperatures required to achieve suitable levels of reduction introduce challenges in reactor design and operation, leading to efficiency penalties. Here, we provide a quantitative assessment of the thermodynamic and kinetic properties of La 1-xSrxMnO3-δ perovskites, targeted for a reduced temperature operation of thermochemical water splitting. Sr-doping into lanthanum manganite increases the thermodynamic fuel production capacity, which reaches 9 ml g-1 for 0.4 Sr for a thermochemical cycle operated between 1400 and 800 °C. The hydrogen yields are moreover in good agreement with expected values based on analysis and extrapolation of thermogravimetric data available in the literature. High levels of Sr doping, however, result in low steam-to-hydrogen conversion rates, implying high energy penalties in an operational reactor. Furthermore, the rate of fuel production decreases with increasing Sr content, suggesting that intermediate compositions may yield the most suitable combination of properties. This journal is. |
| 17. | Shunta Nishioka, Yasuomi Yamazaki, Megumi Okazaki, Keita Sekizawa, Go Sahara, Riho Murakoshi, Daiki Saito, Ryo Kuriki, Takayoshi Oshima, Junji Hyodo, Yoshihiro Yamazaki, Osamu Ishitani, Thomas E. Mallouk, Kazuhiko Maeda, Defect Density-Dependent Electron Injection from Excited-State Ru(II) Tris-Diimine Complexes into Defect-Controlled Oxide Semiconductors, Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b09781, 123, 46, 28310-28318, 2019.11, Dye-sensitized solar cells and photocatalysts that consist of a light-absorbing dye and a wide gap oxide semiconductor substrate have been studied extensively as a means of solar energy conversion. Although defects existing at an oxide surface have a significant impact on the electron injection efficiency from the excited state dye-molecule into the oxide, the effects of defects on the electron injection process have not been fully understood in any dye-sensitized system. In this study, we present a systematic evaluation of electron injection into defects using emissive Ru(II) complexes adsorbed on oxide substrates (HCa2Nb3O10 nanosheets and nonstoichiometric SrTiO3-δ), which had different defect densities. Using these oxides, electron injection from adsorbed Ru(II) complexes was observed by time-resolved emission spectroscopy. It was shown that electron injection from the excited state Ru(II) complex into an oxide was influenced by the defect density of the oxide as well as by the excited state oxidation potential (Eox*) of the Ru(II) complex. Electron injection was clearly accelerated with increasing defect density of the oxide, and was inhibited with increasing electron density of the oxide because of a trap-filling effect. Even though the Eox∗ of the Ru(II) complex was more positive than the conduction band edge potential of the oxide, electron injection into defects could be identified when a defective oxide was employed. The electron injection event is discussed in detail, on the basis of the defect density and the energy levels of oxides as well as the Eox∗ values of the Ru(II) complexes. Overall, the results suggest that it is possible to estimate the potential of surface defect states in oxide by changing Eox∗ of an emissive complex dye.. |
| 18. | P. Phu, K. Yamanoi, K. Ohnishi, J. Hyodo, K. Rogdakis, Y. Yamazaki, T. Kimura, H. Kurebayashi, Bolometric ferromagnetic resonance techniques for characterising spin-Hall effect at high temperatures, Journal of Magnetism and Magnetic Materials, 10.1016/j.jmmm.2019.04.070, 485, 304-307, 2019.09, We report on current-induced ferromagnetic resonance techniques to characterise spin-Hall effect at high temperatures. A microwave current was injected into a patterned CoFeB/Pt bi-layer grown on a glass substrate, simultaneously exerting spin-transfer torques through the spin-Hall effect and also causing Joule heating enabling the control of the device temperature. We measured the device temperature by using the device itself as a local temperature sensor. A clear reduction of CoFeB magnetisation was observed as the device temperature was increased allowing us to estimate the Curie temperature of our CoFeB film to be 920 K. The spin-Hall angle of Pt was quantified as (1.72 ± 0.03) × 10−2 at 300 K and was slightly increased to (1.75 ± 0.02) × 10−2 at 410 K. This simple method can be widely used for quantifying the spin-Hall angle of a large variety of materials at high temperatures.. |
| 19. | E. Kim, Y. Yamazaki, S. M. Haile, H. I. Yoo, Effect of NiO sintering-aid on hydration kinetics and defect-chemical parameters of BaZr0.8Y0.2O3 - Δ, Solid State Ionics, 10.1016/j.ssi.2015.01.001, 275, 23-28, 2015.07, The influence of NiO, used as a sintering aid, on the transport properties of BaZr0.8Y0.2O3 - Δ was investigated by monitoring electrical conductivity relaxation of specimens with and without NiO during hydration in atmospheres of different oxygen activities at 700 and 800 °C. The chemical diffusivities of H and O governing the kinetics were precisely evaluated from the transient conductivity, and all the defect-chemical parameters - the two external equilibrium constants and mobilities of all the carriers, VO· ·, Hi· and h· - were determined from the steady-state equilibrium conductivity. It is found that the processing benefits afforded by NiO are accompanied by a significant reduction in ionic mobilities and hydration reaction constant. These factors, in turn, result in a smaller electrolytic regime in the presence of NiO than when it is absent.. |
| 20. | Frédéric Blanc, Luke Sperrin, Daniel Lee, Riza Dervişoǧlu, Yoshihiro Yamazaki, Sossina M. Haile, Gaël De Paëpe, Clare P. Grey, Dynamic nuclear polarization NMR of low-γ nuclei Structural insights into hydrated yttrium-doped BaZrO3, Journal of Physical Chemistry Letters, 10.1021/jz5007669, 5, 14, 2431-2436, 2014.07, We demonstrate that solid-state NMR spectra of challenging nuclei with a low gyromagnetic ratio such as yttrium-89 can be acquired quickly with indirect dynamic nuclear polarization (DNP) methods. Proton to 89Y cross polarization (CP) magic angle spinning (MAS) spectra of Y3+ in a frozen aqueous solution were acquired in minutes using the AMUPol biradical as a polarizing agent. Subsequently, the detection of the 89Y and 1H NMR signals from technologically important hydrated yttrium-doped zirconate ceramics, in combination with DFT calculations, allows the local yttrium and proton environments present in these protonic conductors to be detected and assigned to different hydrogen-bonded environments.. |
| 21. | Yoshihiro Yamazaki, Chih Kai Yang, Sossina M. Haile, Unraveling the defect chemistry and proton uptake of yttrium-doped barium zirconate, Scripta Materialia, 10.1016/j.scriptamat.2010.12.034, 65, 2, 102-107, 2011.07, A review of the experimental literature documenting water uptake in yttrium-doped barium zirconate in combination with new results obtained here show that much of the observed scatter can be explained in terms of barium deficiency, which furthermore induces a lowering in cell volume. In addition, through a comparison of weight changes under regular and heavy water vapor pressure, strong evidence is found for bulk oxidation of the oxide by water simultaneous with hydration.. |
| 22. | A. Suino, Y. Yamazaki, H. Nitta, K. Miura, H. Seto, R. Kanno, Y. Iijima, H. Sato, S. Takeda, E. Toya, T. Ohtsuki, Tracer diffusion of Cu in CVD β-SiC, Journal of Physics and Chemistry of Solids, 10.1016/j.jpcs.2007.07.007, 69, 2-3, 311-314, 2008.02, Tracer diffusion coefficients of 67Cu and 64Cu in CVD β-Silicon carbide (β-SiC) have been measured in the temperature range between 623 and 1373 K by use of a serial ion-beam sputter-microsectioning technique. The temperature dependence of the diffusion coefficient D is expressed by DCu* = 8 . 2- 0.5+ 0.5 × 1 0- 16 exp (- 41 ± 1 kJ mol- 1 / RT) m2 s- 1 . The diffusion coefficient of Cu in β-SiC is larger than those of Si and C by more than six orders of magnitude and those of Fe and Cr by one-three orders of magnitude. The activation energy for the diffusion of Cu is about one twentieth of that for the self-diffusion. The results suggest that an interstitial mechanism operates on the diffusion of Cu in β-SiC.. |
| 23. | S. Takemoto, H. Nitta, Y. Iijima, Y. Yamazaki, Diffusion of tungsten in α-iron, Philosophical Magazine, 10.1080/14786430600732093, 87, 11, 1619-1629, 2007.04, Tracer diffusion coefficient of 181W in -iron has been determined in the temperature range between 833 and 1173 K using a serial sputter-microsectioning method. The temperature dependence of the diffusion coefficient, D, over the whole temperature range of -iron across the Curie temperature (TC = 1043 K), can be expressed by [image omitted] where s is the ratio of the spontaneous magnetization at T K to that at 0 K. The factor 0.086 in the above equation is smaller than 0.156 for the self-diffusion, showing that the influence of the magnetic transformation on the diffusion of tungsten in -iron is smaller than that on the self-diffusion. The activation energy 287 kJ/mol for tungsten diffusion in the paramagnetic iron is much higher than 250.6 kJ/mol for the self-diffusion. Atomic size effect is predominant in the activation energies for diffusion of transition elements in the paramagnetic -iron.. |
| 24. | Takahiro Iida, Yoshihiro Yamazaki, Takayuki Kobayashi, Yoshiaki Iijima, Yuh Fukai, Enhanced diffusion of Nb in Nb-H alloys by hydrogen-induced vacancies, Acta Materialia, 10.1016/j.actamat.2005.02.049, 53, 10, 3083-3089, 2005.06, The diffusion coefficient of 95Nb in pure Nb and Nb-H alloys whose hydrogen concentration ranges between H/Nb = 0.05 and 0.34 in atomic ratio has been determined in the temperature range 823-1598 K using a serial sputter-microsectioning technique. The diffusion coefficient of Nb in the Nb-H alloys was found to increase significantly with increasing hydrogen concentration. The dependence of the diffusion enhancement on temperature and hydrogen concentration was examined in some detail, and explained tentatively in terms of average occupation number of hydrogen atoms per vacancy, r. The diffusion enhancement comes primarily from the decrease of the activation energy Q, resulting from the increase of r with increase of hydrogen concentration. Some remaining problems with this interpretation are pointed out for future investigations.. |
| 25. | Yoshiaki Iijima, Hiroyuki Nitta, Ryusuke Nakamura, Koichi Takasawa, Akiko Inoue, Shigeru Takemoto, Yoshihiro Yamazaki, Precise measurement of low diffusion coefficients using radioactive tracers, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.69.321, 69, 4, 321-331, 2005.04, Experimental techniques for precise determination of low tracer diffusion coefficients in solid metals and alloys using radioisotopes are reviewed. Sputter-microsectioning method is most useful to measure submicron diffusion profiles at low temperatures. Measurements of tracer diffusivity along grain boundaries and dislocations in iron and stainless steels from the analysis of type C kinetics as well as type B kinetics are discussed.. |
| 26. | Yoshihiro Yamazaki, Takahiro Iida, Yoshiaki Iijima, Yuh Fukai, Diffusion of Nb in Nb-H alloys, Defect and Diffusion Forum, 237-240, PART 1, 346-351, 2005.01, Self-diffusion coefficient of 95Nb in NbHx alloys (x=0.05, 0.25 and 0.3) has been determined in the temperature range from 823 to 1323 K by using a serial sputter-microsectioning technique. The self-diffusion coefficient of Nb in the NbHx alloys are larger than that in Nb, suggesting that vacancies are formed by hydrogen dissolution, that is, the formation of hydrogen-induced vacancies. The value of the pre-exponential factor for the Nb diffusion in the NbH0.05 alloy is five times larger than that in Nb, while the difference in the activation energies between the NbH 0.05 alloy and pure Nb is small. The self-diffusion enhancement in the NbH0.05 alloy is mainly caused by lowering in vibrational frequencies of atoms in the immediate neighborhood of hydrogen-induced vacancies.. |
| 27. | Masaki Mizouchi, Yoshihiro Yamazaki, Yoshiaki Iijima, Koji Arioka, Low temperature grain boundary diffusion of chromium in SUS316 and 316L stainless steels, Materials Transactions, 10.2320/matertrans.45.2945, 45, 10, 2945-2950, 2004.10, Grain boundary diffusivity of chromium in SUS316 and 316L stainless steels has been determined in the temperature range between 518 and 1173 K. The magnitudes of the grain boundary diffusivities in four kinds of specimens are in the order of the cold-worked SUS316, the solution-treated SUS316L, the solution-treated SUS316 and the sensitized SUS316. The grain boundary diffusivities in these specimens are remarkably higher than those of previous works. The activation energies for the former are 85-91 kJmol-1, whereas those for the latter are 151-234 kJmol-1.. |
| 28. | Hiroyuki Nitta, Yoshiaki Iijima, Kazumi Tanaka, Yoshihiro Yamazaki, Chan Gyu Lee, Takashi Matsuzaki, Tadao Watanabe, Grain boundary self-diffusion in directionally solidified equiatomic Fe-Co alloy, Materials Science and Engineering A, 10.1016/j.msea.2004.05.056, 382, 1-2, 250-256, 2004.09, Grain boundary diffusivities of 59Fe and 57Co in a binary Fe-50 at.%Co alloy have been determined at a temperature range between 883 and 1123 K by serial sputter-microsectioning technique using specimen unidirectionally solidified at three different solidification rates of 12000, 60 and 32 mm/h. Above the order-disorder transformation temperature of 1003 K, the Arrhenius plots of the grain boundary diffusivities in the alloy solidified at three rates show straight lines. The diffusivities in the specimen with 32 mm/h are higher than those with 60 and 12000 mm/h. Below 1003 K, all the Arrhenius plots of the diffusivities show downward curvature remarkably owing to the atomic ordering. From the analysis of depth profiles, the atomic ordering gives large influence on the diffusion along subgrain boundaries rather than the diffusion along random grain boundaries.. |
| 29. | Hiroyuki Nitta, Yoshiaki Iijima, Kazumi Tanaka, Yoshihiro Yamazaki, Chan Gyu Lee, Takashi Matsuzaki, Tadao Watanabe, Self-diffusion in unidirectionally solidified Fe-50 at.% Co alloys at 833-1123 K, Materials Science and Engineering A, 10.1016/j.msea.2004.05.055, 382, 1-2, 243-249, 2004.09, The self-diffusion coefficients DFe and DCo of radioactive tracers 59Fe and 57Co, respectively, in a binary Fe-50 at.% Co alloy were experimentally determined for the disordered (α) phase with the body-centered cubic (bcc) structure and the ordered (α′) phase with the B2 structure using specimens solidified unidirectionally at solidification rates of 32, 60 and 12,000 mm/h. These specimens were electroplated with the tracers and then heat treated at a temperature range between 883 and 1123 K for various times of 1.5 × 103-1.204 × 106 s. Penetration profiles of the tracers in the heat treated specimen were measured by a serial sputter-microsectioning technique. The measurement implies that the penetration of each tracer is controlled by the volume diffusion. As to the α phase, the values of DFe and D Co coincide well with those obtained by lijima and Lee using well annealed polycrystalline specimens of a binary Fe-50 at.% Co alloy. On the other hand, D Fe and D Co in the α′ phase are greater for the unidirectionally solidified specimen than for the well-annealed polycrystalline specimen. Such greater values of D Fe and D Co are attributed to the contribution of the dislocation diffusion.. |
| 30. | Yoshihiro Yamazaki, Yoshiaki Iijima, Masuo Okada, Diffusion of Fe in Au under elevated H2 pressure, Philosophical Magazine Letters, 10.1080/09500830310001655202, 84, 3, 165-174, 2004.03, The diffusion coefficient DFe* of Fe in Au under a H 2 pressure of 5GPa has been determined in the temperature range from 1004 to 1301K by relating the interdiffusion coefficients in single-phase Au-(Au-Fe) couples with the Darken-Manning relation. The value of D Fe*, in Au at 130IK under a H22 pressure of 5 GPa is three times that under a pressure of 5 GPa without H2, whereas the former is one tenth of that under a He pressure of 0.1 MPa. The temperature dependence of DFe* in Au under a H2 pressure of 5 GPa can be expressed as DFe* = 7.8-5.6 +20 × 10-6 exp(-195 ± 12 kJ mol -1/RT) m2 s-1. The pre-exponential factor is nearly equal to that in He at 0.1 MPa, although the activation energy is only 21 kJ mol-1 larger than that observed in He at 0.1 MPa. This behaviour contrasts with that in γ-Fe, which has a very high solubility of H2 under high pressures.. |
| 31. | Yoshihiro Yamazaki, Yoshiaki Iijima, Masuo Okada, Enhanced diffusion of Au in γ-Fe by vacancies induced under elevated hydrogen pressure, Acta Materialia, 10.1016/j.actamat.2003.11.008, 52, 5, 1247-1254, 2004.03, The diffusion coefficients of Au, DAu*, in γ-Fe in the temperature range from 1263 to 1653 K at 0.1 MPa Ar and from 1207 to 1351 K at 3-5 GPa H2 have been determined by relating the interdiffusion coefficients in single-phase Fe/Fe-Au couples with the Darken-Manning relation. The value of DAu* in γ-Fe at 5 GPa H2 is 2-3 times larger than that at 0.1 MPa Ar. The temperature dependence of D Au* in γ-Fe at 0.1 MPa Ar and at 5 GPa H2 can be expressed as DAu*=8.1-2.3 +3.2×10-5exp{-(290±4)kJmol-1/RT} m2 s-1 and DAu*=1.4×10 -3exp(-310kJmol-1/RT) m2 s-1, respectively. The value of the activation energy at 5 GPa H2 is 20 kJ mol-1 larger than that at 0.1 MPa Ar, whereas the value of the pre-exponential factor at 5 GPa H2 is 17 times larger than that at 0.1 MPa Ar. Therefore, the enhancement of the diffusion at 5 GPa H2 is attributed to a high value of activation entropy.. |
| 32. | Yoshihiro Yamazaki, Yoshiaki Iijima, Enhanced diffusion in y-Fe and Au by vacancies induced under elevated hydrogen pressure, Defect and Diffusion Forum, 10.4028/www.scientific.net/ddf.233-234.115, 233-234, 115-126, 2004, Japan. Diffusion in a metal under an elevated hydrogen pressure is interesting in view of the fact that the diffusion is enhanced owing to the injection of a large amount of vacancies into the metal. This is peculiar to an elevated hydrogen pressure because diffusion in a metal is generally suppressed under a hydrostatic pressure. In the present article, the effect of an elevated hydrogen pressure on interdiffusion and impurity diffusion is reviewed in the Au-Fe system which has a large difference in the hydrogen solubilities between γ -Fe and Au under an elevated hydrogen pressure.. |
| 33. | R. Kanno, T. Wada, Y. Yamazaki, J. Wang, M. Isshiki, Y. Iijima, Self-diffusion of cadmium in cadmium telluride annealed in tellurium-saturated atmosphere, Materials Science in Semiconductor Processing, 10.1016/j.mssp.2003.07.020, 6, 5-6, 319-322, 2003.10, Diffusion behavior of Cd in volume and along dislocations in high-purity CdTe annealed in Te-saturated atmosphere has been studied by the radioactive tracer method with a serial ion-beam sputter-microsectioning technique. The temperature dependence of volume diffusion coefficients shows a bend around 773K, whereas that of the self-diffusion along dislocations shows a straight line. This suggests that the defect induced by impurities enhances the volume diffusion but does not affect the diffusion along dislocations.. |
| 34. | Kohta Asano, Yoshihiro Yamazaki, Yoshiaki Iijima, Hydriding and dehydriding processes of LaNi5-xCox (x = 0-2) alloys under hydrogen pressure of 1-5 MPa, Intermetallics, 10.1016/S0966-9795(03)00103-1, 11, 9, 911-916, 2003.09, The hydriding and dehydriding behavior of LaNi5-xCox (0≤x≤2) was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1-5 MPa in the temperature range from 323 to 573 K. In the heating run of the LaNi5-H2 system, two endothermic peaks were observed. One was the peak for the transformation from the γ phase (LaNi5H6 hydride) to the β phase (LaNi5H3 hydride). The other was the peak for the transformation from the β phase to the α phase (solid solution). In the cooling run, one exothermic peak for the transformation from the α phase to the γ phase was observed. In the range of x≤0.5, PDSC curves similar to that of the LaNi5-H2 system were observed. However, in the range of x≥1, one endothermic and one exothermic peaks were observed in the heating and cooling runs, respectively. Using Ozawa's method, the activation energies for the dehydriding processes were estimated. The activation energy for the γ-β transformation was higher than that for the β-α transformation and the activation energy for the β-α transformation has a maximum at the composition of about x = 1.. |
| 35. | Ryusuke Nakamura, Yoshihiro Yamazaki, Yoshiaki Iijima, Interdiffusion in B2 type intermetallic compound FeAl under high pressures, Materials Transactions, 10.2320/matertrans.44.78, 44, 1, 78-82, 2003.01, Interdiffusion coefficient in the B2 FeAl phase at 46-50 at%Al has been measured in the temperature range from 1173 to 1473 K under the pressure from 0.1 MPa to 5 GPa. The activation volume for interdiffusion, ΔV̄, derived from the pressure dependence of interdiffusion coefficient is found to be 0.58-0.90Vm (Vm: molar volume of alloys), which is comparable to or larger than 0.4-0.6Vm for the monovacancy mechanism in bcc pure metals or random alloys. The value of ΔV̄ increases with increasing temperature and also with deviating from stoichiometry, suggesting that divacancy contributes to the diffusion in higher temperatures and in the region of off-stoichiometry.. |
| 36. | H. Nitta, T. Yamamoto, R. Kanno, K. Takasawa, T. Iida, Yoshihiro Yamazaki, S. Ogu, Y. Iijima, Diffusion of molybdenum in α-iron, Acta Materialia, 10.1016/S1359-6454(02)00229-X, 50, 16, 4117-4125, 2002.09, Tracer diffusion coefficient of molybdenum in α-iron was determined in the temperature range between 833 and 1163 K by using a serial sputter-microsectioning technique. The temperature dependence of the diffusion coefficient, D, in the whole temperature range of α-iron across the Curie temperature was found out. Results showed that the influence of the magnetic transformation on the diffusion of molybdenum in α-iron was smaller than that on the self-diffusion as expected from the negative magnetic moment of molybdenum.. |
| 37. | Kohta Asano, Yoshihiro Yamazaki, Yoshiaki Iijima, Hydrogenation and dehydrogenation behavior of LaNi5-x Cox (x = 0, 0.25, 2) Alloys studied by pressure differential scanning calorimetry, Materials Transactions, 10.2320/matertrans.43.1095, 43, 5, 1095-1099, 2002.05, The hydrogenation and dehydrogenation behavior of LaNi5, LaNi4.75 Co0.25 and LaNi3Co2 was studied by the pressure differential scanning calorimetry (PDSC) at the hydrogen pressure range of 1 to 5 MPa in the temperature range from 323 to 473 K with the heating and cooling rates of 2 to 30 K min-1. In the heating run of the hydride of LaNi5, two endothermic peaks were observed. One was the peak for the transformation from the γ phase (full hydride LaNi5H6) to the β phase (hydride LaNi5H3). The other was the peak for the transformation from the β phase to the α phase (solid solution). In the cooling run, one exothermic peak for the transformation from the α phase to the γ phase was observed. These endothermic and exothermic peaks shifted to higher temperatures with the increase in hydrogen pressure. In the heating and cooling runs of the LaNi4.75Co0.25-H2 system the PDSC curves similar to those of the LaNi5-H2 system were observed. However, in the heating run of the hydride of LaNi3Co2 only one endothermic peak was observed. Using Ozawa's method, the activation energies for dehydrogenation of the hydrides were estimated. The activation energy for the γ-β transformation was higher than that for the β-α transformation. Substitution of cobalt for a part of nickel in LaNi5 increased the activation energies for the phase transformations.. |
| 38. | K. Irisawa, A. Fujita, K. Fukamichi, Y. Yamazaki, Y. Iijima, Influence of nitrogen on the magnetovolume effects in La(Fe xAl 1-x) 13 compounds, Journal of Applied Physics, 10.1063/1.1452711, 91, 10 I, 8882-8884, 2002.05, Nitrogen and hydrogen absorptions have been carried out in order to discuss the influence of interstitial atoms on the magnetovolume effects for the La(Fe xAl 1-x) 13 (x=0.83 and 0.86) compounds. The average magnetic hyperfine field and the Curie temperature T C of nitrides are lower than that of hydrides. The volume expansion due to the nitrogen absorption is about twice that due to the hydrogen absorption. Comparing the change in T C of the nitrides with that of hydrides and the pressure effect on T C, the hybridization between the Fe 3d and N 2p orbital should be taken into consideration in the lower T C of nitrides.. |
| 39. | Koichi Takasawa, Yoshihiro Yamazaki, Seiichi Takaki, Kenji Abiko, Yoshiaki Iijima, Diffusion of Cr and Fe in a high-purity Fe-50 mass% Cr-8 mass% W alloy, Materials Transactions, 10.2320/matertrans.43.178, 43, 2, 178-181, 2002.02, Volume and grain boundary diffusivities of 51Cr and 59Fe in a high purity Fe-50 mass% Cr-8 mass% W (Fe-50Cr-8W) alloy have been determined in the temperature range between 1023 and 1373 K with the sputter-microsectioning technique. The volume diffusion coefficients of Cr and Fe in the Fe-50Cr-8W alloy are smaller than those in a high-purity Fe-50 mass% Cr (Fe-50Cr) alloy. Linear Arrhenius lines for the volume self-diffusion coefficients of both tracers have been observed in the temperature range examined. The activation energies for the volume diffusion of both components in the Fe-50Cr-8W alloy are somewhat smaller than those in the Fe-50Cr alloy. On the other hand, the grain boundary diffusivities of Cr and Fe in the Fe-50Cr-8W alloy at 1123 K are about two orders of magnitude smaller than those in the Fe-50Cr alloy.. |
| 40. | Yumiko Shima, Yukio Ishikawa, Hiroyuki Nitta, Yoshihiro Yamazaki, Kouji Mimura, Minoru Isshiki, Yoshiaki Iijima, Self-diffusion along dislocations in ultra high purity iron, Materials Transactions, 10.2320/matertrans.43.173, 43, 2, 173-177, 2002.02, Self-diffusion along dislocations in ultra high purity iron containing 0.5-1.2 mass ppm carbon, 0.1-1.0 mass ppm nitrogen and 1.8-4.0 mass ppm oxygen has been studied by the radioactive tracer method with the sputter-microsectioning technique. Below 700 K, the self-diffusion coefficient along dislocations has been determined directly from the type C kinetics classified by Harrison, whereas above 800 K it has been obtained by the type B kinetics assuming that the effective radius of dislocation pipe is equal to 5 × 10-10 m. The temperature dependence of the self-diffusion coefficient along dislocations does not show a linear Arrhenius relation. Below 900 K the Arrhenius plot shows slightly downward curvature. However, above 900 K the self-diffusion coefficient along dislocations increases remarkably with increasing temperature. The value at 900 K is 10-14 m2s-1, while it takes 10-10 m2s-1 at the Curie temperature (1043 K). It seems that the steep increase of the self-diffusion coefficient along dislocations near the Curie temperature is related to the magnetic transformation in ultra high purity iron.. |
| 41. | R. Nakamura, K. Takasawa, Y. Yamazaki, Y. Iijima, Single-phase interdiffusion in the B2 type intermetallic compounds NiAl, CoAl and FeAl, Intermetallics, 10.1016/S0966-9795(01)00125-X, 10, 2, 195-204, 2002.02, Interdiffusion coefficients, D̃, in the B2 type NiAl, CoAl and FeAl phases have been determined by single phase diffusion couples over a wide temperature range from 1073 to 1773 K. The value of D̃ in the NiAl and CoAl phases shows a minimum at about 47 at.% Al deviating slightly from the stoichiometric composition, while the value of D̃ in the FeAl phase has a weak minimum at about 41 at.% Al. The value of the activation energy, Q̃, for interdiffusion in the NiAl and CoAl phases shows a maximum at about 47 at.% Al, where the value of Q̃ in the CoAl phase is much higher than that in the NiAl phase, while the value of Q̃ in the FeAl phase is nearly constant and much lower than those in the other two phases. It is observed that the larger the lattice constant of the compounds becomes, the lower the activation energy for diffusion in the compounds becomes. Thus, the magnitude of activation energy for diffusion in the B2 type NiAl, CoAl and FeAl is probably related to the lattice constant of the compounds. Using the interdiffusion coefficient and the tracer diffusion coefficients of Ni and Fe with the help of Darken's relation, the diffusion coefficient of Al in the NiAl and FeAl phases has been estimated.. |
| 42. | Yoshihiro Yamazaki, M. Sugihara, S. Takaki, K. Abiko, Y. Iijima, Certification of high purity metals as primary reference materials - A challenge for multielement trace analysis, 7th International Conference on Ultra-High-Purity Base Metals (UHPM-2000) Physica Status Solidi (A) Applied Research, 10.1002/1521-396X(200201)189:13.0.CO;2-1, 189, 1, 107-122, 2002.01, The Bundesanstalt für Materialforschung und -prüfung (Federal Institute for Materials Research and Testing) (BAM) is establishing a system of primary reference materials to meet the demands for metrological traceability and to act as national standards in the field of elemental analysis. For all elements of the periodic table - except those that are gases or radioactive - two different kinds of reference materials are being certified. One is for analyte calibration (Type A) and one for problems concerning matrix matching (Type B). These substances are of very high purity and of defined stoichiometry. As far as possible, pure elements and metals rather than pure compounds are used. The certification of both types of material requires most elements of the periodic table to be certified at very low levels using trace element analysis methods. The application of these methods is described and examples of the certification of copper and iron are given.. |
| 43. | Asaya Fujita, Shun Fujieda, Kazuaki Fukamichi, Yoshihiro Yamazaki, Yoshiaki Iijima, Giant magnetic entropy change in hydrogenated La(Fe0.88Si0.12)13Hy compounds, Materials Transactions, 10.2320/matertrans.43.1202, 43, 5, 1202-1204, 2002.01, A magnetic entropy change ΔSM due to the itinerant-electron metamagnetic (IEM) transition was estimated to be -23 J/kg K around the Curie temperature for La(Fe0.88Si0.12)13 in the magnetic field change from 0 to 5 T. In order to control the Curie temperature while keeping such a large value of ΔSM, hydrogen absorption was carried out. La(Fe0.88Si0.12)13H1.0 with TC = 274 K shows a large ΔSM due to the IEM transition around room temperature. The adiabatic temperature change ΔTad from 0 to 2 T is about 7 K, comparable to that of Gd5(Ge0.5Si0.5)4. By changing the hydrogen concentration, the Curie temperature can be controlled from 195 to 336 K. It should be noted that the magnitude of ΔSM is almost the same after hydrogen absorption. Therefore, the hydrogenated La(Fe0.88Si0.12)13Hy compounds are promising magnetic refrigerants working in a wide range of temperature.. |
| 44. | S. Fujieda, A. Fujita, K. Fukamichi, Yoshihiro Yamazaki, Y. Iijima, Giant isotropic magnetostriction of itinerant-electron metamagnetic La(Fe0.88Si0.12)13Hy compounds, Applied Physics Letters, 10.1063/1.1388157, 79, 5, 653-655, 2001.07, La(FexSi1-x)13 compounds exhibit an itinerant-electron metamagnetic (IEM) transition above Curie temperature TC. The IEM transition in the compound with x=0.88 is accompanied by a giant volume change. From a practical viewpoint, TC was controlled by hydrogen absorption in order to obtain such a giant volume magnetostriction at room temperature. For the La(Fe0.88Si0.12)13H1.0 compound, the IEM transition occurs above TC = 278 K, and a significant isotropic linear magnetostriction of about 0.3% at 7 T is induced in the vicinity of room temperature. This large magnetostriction is attributed to the giant volume magnetostriction of about 1% by the IEM transition.. |
| 45. | K. Takano, H. Nitta, H. Seto, C. G. Lee, K. Yamada, Y. Yamazaki, H. Sato, S. Takeda, E. Toya, Y. Iijima, Volume and dislocation diffusion of iron, chromium and cobalt in CVD β-SiC, Science and Technology of Advanced Materials, 10.1016/S1468-6996(01)00015-8, 2, 2, 381-388, 2001.06, Impurity tracer diffusion of 59Fe, 51Cr and 57Co in CVD β-SiC has been studied in the temperature range between 973 and 1873 K. The temperature dependence of the volume diffusion coefficients of iron and chromium can be expressed by linear Arrhenius equations. The preexponential factor and the activation energy are estimated to be 8.7 × 10-15 m2 s-1 and 111 kJ mol-1 for iron, respectively, and 9.5 × 10-15 m2 s-1 and 81 kJ mol-1 for chromium, respectively. The diffusion coefficients of iron and chromium are much higher than those of the self-diffusion in β-SiC. Furthermore, the activation energies for the diffusion of iron and chromium are about one-tenth of those for carbon and silicon in β-SiC. Therefore, it seems that an interstitial mechanism is predominant for the diffusion of iron and chromium in β-SiC. On the other hand, the diffusion coefficient of cobalt above 1673 K is higher than that of iron, while at lower temperatures it is much lower than that of iron. The difference in the diffusion coefficients at 1173 K is more than three orders of magnitude. Thus, the temperature dependence of the diffusion coefficients of cobalt shows a strongly curved Arrhenius relation. This suggests that cobalt atoms diffuse by an interstitial mechanism at higher temperatures and by a substitutional mechanism at lower temperatures. From the deeper regions of the penetration profiles of iron, chromium and cobalt the dislocation diffusion coefficients of them have been estimated.. |
| 46. | K. Irisawa, A. Fujita, K. Fukamichi, Y. Yamazaki, Y. Iijima, E. Matsubara, Change in the magnetic state of antiferromagnetic La(Fe0.88Al0.12)13 by hydrogenation, Journal of Alloys and Compounds, 10.1016/S0925-8388(00)01468-7, 316, 1-2, 70-74, 2001.03, The change in magnetic properties of La(Fe0.88 Al0.12)13 by hydrogenation has been investigated. The NaZn13-type structure is preserved and the lattice constant is increased after hydrogenation, showing that the hydrogen atoms intrude into the position between the icosahedral clusters and La atoms. By hydrogenation, the magnetic ground state is changed from the antiferromagnetic to the ferromagnetic state, accompanied by significant increases in the spontaneous magnetic moment and the Curie temperature.. |
| 47. | Y. Yamazaki, H. Kakuta, M. Okada, Y. Iijima, Interdiffusion in Au / Fe couples under elevated hydrogen pressures, Defect and Diffusion Forum, 10.4028/www.scientific.net/ddf.194-199.1069, 194-199 PART 2, 1069-1074, 2001.01, The interdiffusion coefficients D̃ in the Au/γ-Fe two-phase and the Au/Au-37at%Fe single-phase couples have been determined under the hydrostatic pressure (HP) and hydrostatic hydrogen pressure (HHP) of 5 GPa at 1263 K. The value of D̃ in the Au-rich phase of the Au/γ-Fe couple under the HHP of 5 GPa is 4 times larger than that under the HP of 5 GPa, while the value of D̃ in the γ-Fe phase under the HHP is 50 times larger than that under the HP, implying that the concentration of vacancies injected by the HHP into the γ-Fe phase is much larger than that into the Au-rich phase. The enhancement of the interdiffusion in the Au/γ-Fe couple by the HHP of 5 GPa is attributed to the enlargement of vacancy flow from the γ-Fe phase towards the Au-rich phase in the couple.. |
| 48. | K. Asano, T. Tabata, Y. Yamazaki, Y. Iijima, Protium diffusion in LaNi5 alloy, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.65.9_803, 65, 9, 803-806, 2001.01, Diffusion of protium in the α phase (solid solution), the ά phase (α phase dehydrided from the β phase) and the β phase (hydride) of LaNi5-H alloys was studied by the desorption method. It was observed that the diffusion coefficient of protium in the β phase was a little higher than that in the α phase and that these were much higher than that in the ά phase. The difference between the diffusion coefficients in the three phases is attributed to the difference in the protium concentration between the α phase and the β phase and to the difference in the trapping density between the α phase and the ά phase.. |
| 49. | Osamu Taguchi, Tomoni Watanobe, Yoshihiro Yamazaki, Yoshiaki Iijima, Reaction diffusion in the Au-Ti system between 1110K and 1150K, Defect and Diffusion Forum, 10.4028/www.scientific.net/ddf.194-199.1569, 194-199 PART 2, 1569-1574, 2001, The growth kinetics of the intermetallic compounds and of the β-Ti phase in the diffusion couples composed of Au and α-Ti were investigated in the narrow temperature range between the eutectoid temperature (α-Ti, β-Ti and AuTi3 ) and the temperature of the α-β allotropic transformation of Ti. Four intermetallic compounds, Au4Ti, Au2Ti, AuTi and AuTi3, predicted from the Au-Ti phase diagram have been observed in the diffusion zone. The Au2Ti and AuTi3 phases are not the stoichiometric compounds but have a narrow concentration range of about 1 at%. The layer growth of the four intermetallic compounds and the β-Ti phase obeys a parabolic law, namely the value of time exponent of layer growth is nearly equal to 1/2. The layer growth of the β-Ti phase is much faster than that of intermetallic phases. The Arrhenius relation of the growth rate constants of these layers have been observed. The activation energies for the layer growth of intermetallic compounds are found to be extremely high.. |
| 50. | Motohide Sugihara, Yoshihiro Yamazaki, Seiichi Takaki, Kenji Abiko, Yoshiaki Iijima, Self-diffusion in high purity Fe-50 mass%Cr alloy, Materials Transactions, JIM, 10.2320/matertrans1989.41.87, 41, 1, 87-90, 2000.01, Tracer self-diffusion coefficients of 51Cr and 59Fe in a high purity Fe-50 mass%Cr alloy have been determined in the temperature range between 923 and 1273 K by use of the sputter-microsectioning technique. A linear Arrhenius line has been observed for each self-diffusion across the α-σ phase transformation temperature 1103 K, which is consistent with the suppression of the σ phase formation by purification. The Arrhenius equations can be expressed by DCr = 0.54 × 10-4 exp(-251 kJ mol-1/RT)m2 s-1 and DFe = 0.30 × 10-4 exp(-243 kJ mol-1/RT) m2 s-1. The activation energies for the self-diffusion of Cr and Fe by the present work are much lower than 293 and 312 kJ mol-1 determined previously by Paxton et al. in the temperature range from 1223 to 1523 K, respectively.. |
| 51. | Yoshihiro Yamazaki, K. Takano, H. Takamura, S. Sugimoto, M. Homma, M. Okada, Magnetic properties of Sm-Co-Cu and Sm-Co-Cu/Co exchange-spring films with high coercivity, materials transactions, jim, 10.2320/matertrans1989.39.302, 39, 2, 302-307, 1998.01, The magnetic properties of Sm-Co-Cu films and Sm-Co-Cu/Co multilayered films prepared by rf-sputtering were investigated. The addition of Cu to Sm-Co film had the effect of decrement of crystallization temperature. The Sm28Co39Cu13 film annealed for 1 h at 623 K showed a reversible demagnetization curve with 82% springback ratio of [Mr' -M(H)]/[Mr-M(H)] and a high coercivity of 2480 kA·m-1. This film was found to be an exchange-spring magnet film composed of the hard magnetic phase such as SmCo5 and Sm2Co7 phases and a soft magnetic phase of Co. Sm28Co59Cu13/Co(x nm) multilayered film whose Co thickness was from 0 to 15 nm was also found to be an exchangespring magnet film.. |
| 52. | Yoshihiro Yamazaki, Kazuhide Takano, Hitoshi Takamura, Satoshi Sugimoto, Motofumi Homma, Masuo Okada, Magnetic properties of Sm-Co and Sm-Co/M (M=Co, Fe) exchange-spring films, Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy, 10.2497/jjspm.44.827, 44, 9, 827-832, 1997.09, The structure and magnetic properties of Sm-Co films and Sm-Co/M (M=Co, Fe) multilayered films prepared by rf sputtering were investigated. The results show that a hard magnetic phase as Sm2Co17 and SmCo5 phase and a soft magnetic phase were formed by annealing Sm-Co and Sm-Co/M films. Sm16Co84 film annealed for 1.8 ks at 773 K had the springback ratio of [Mr′-M(H)]/[Mr-M(H)]=0.72. This film was found to behave as a exchange-spring magnet composed of a hard magnetic phase and a soft magnetic phase. Sm16Co84/Fe multilayered film was also found to be a exchange-spring magnet.. |
| 53. | A Kuwabara, CAJ Fisher, Y Okuyama, Y Yamazaki, First principles calculations of defect clustering in acceptor-doped BaZrO3, 2016.01. |
| 54. | Yoshihiro Yamazaki, Solar-driven thermochemical CO2 reduction using nonstoichiometric perovskite, 2016.01. |
| 55. | Michael J. Ignatowich, Alexander H. Bork, Timothy C. Davenport, Jennifer L.M. Rupp, Chih Kai Yang, Yoshihiro Yamazaki, Sossina M. Haile, Impact of enhanced oxide reducibility on rates of solar-driven thermochemical fuel production, MRS Communications, 10.1557/mrc.2017.108, 7, 4, 873-878, 2017.12, Two-step, solar-driven thermochemical fuel production offers the potential of efficient conversion of solar energy into dispatchable chemical fuel. Success relies on the availability of materials that readily undergo redox reactions in response to changes in environmental conditions. Those with a low enthalpy of reduction can typically be reduced at moderate temperatures, important for practical operation. However, easy reducibility has often been accompanied by surprisingly poor fuel production kinetics. Using the La1-xSr xMnO3 series of perovskites as an example, we show that poor fuel production rates are a direct consequence of the diminished enthalpy. Thus, material development efforts will need to balance the countering thermodynamic influences of reduction enthalpy on fuel production capacity and fuel production rate.. |
| 56. | Y.Yamazaki, Y. Iijima, Interdiffusion Coefficients in Fe/Au-Fe Diffusion Couples, Proceedings of Japan Symposium on Thermophysical Properties, 18 , 193-196, 1997.10. |
| 57. | K. Horie, K. Gunji, Y.Yamazaki, Y. Iijima, Non-equilibrium VZr Phase in V-Zr System, Proceedings of Japan Symposium on Thermophysical Properties, 19, 179-182, 1998.10. |
| 58. | T. Sugiyama, Y.Yamazaki, Y. Iijima,, Interdiffusion and Kirkendall Effect in Au/Ni Diffusion Couples, Proceedings of Japan Symposium on Thermophysical Properties, 19 , 175-178, 1998.10. |
| 59. | T. Sugiyama, Y.Yamazaki, Y. Iijima, Interdiffusion in Au/Ni Diffusion Couples, Proceedings of International Conference on Solid-Solid Phase Transformations '99 (JIMIC-3) , 513-516, 1999.05. |
| 60. | Y.Yamazaki, Y. Iijima, Deviation from Darken's Relation in Au/Fe Diffusion Couples, Proceedings of International Conference on Solid-Solid Phase Transformations '99 (JIMIC-3) , 493-496, 1999.05. |
| 61. | Y. Iijima, Y.Yamazaki, Mechanism of Protium Diffusion in High Density Protium Alloys, Proceedings of the First International Symposium on New Protium Function in Materials , 54-63, 1999.06. |
| 62. | H. Nitta, K. Tanaka, Y.Yamazaki, T. Masuzaki, T. Watanabe, Y. Iijima, Effect of Grain Boundary Character Distribution on Grain Boundary Diffusion of Fe and Co in Fe-50at%Co Alloy, Proceedings of Japan Symposium on Thermophysical Properties, 177-180, 1999.12. |
| 63. | R. Nakamura, Y.Yamazaki, Y. Iijima, Determination on Interdiffusion Coefficient in Co-rich CoAl, Proceedings of Japan Symposium on Thermophysical Properties , 173-176, 1999.10. |
| 64. | Y. Hashimoto, K. Asano, Y.Yamazaki, Diffusion of Hydrogen in LaNi5-xAlx Hydrogen Absorbing Alloy, Proceedings of Japan Symposium on Thermophysical Properties , 326-328, 2001.07. |
| 65. | K. Asano, Y.Yamazaki, Y. Iijima, Protium Diffusion in alpha and beta phases of LaNi5-H alloy studied by desorption method, Proceedings of Fourth Pacific Rim International Conference on Advanced Materials and Processing , 433-436, 2001.12. |
| 66. | O. Taguchi, T. Watanabe, Y.Yamazaki, Y. Iijima, Reaction Diffusion in Au-Ti System, Proceedings of Fourth Pacific Rim International Conference on Advanced Materials and Processing (PRICM4), 2325-2328, 2001.12. |
| 67. | R. Nakamura, Y.Yamazaki, Y. Iijima, Intrinsic Diffusion and Diffusion Mechanisms in the B2-NiAl phase, Proceedings of Fourth Pacific Rim International Conference on Advanced Materials and Processing (PRICM4), 855-858, 2001.12. |
| 68. | Y.Yamazaki, H. Kakuta, M. Okada, Y. Iijima, Effect of High Hydrogen Pressure on Interdiffusion in Au/Fe Couple, Advanced Materials and Processing (PRICM4), 2563-2566, 2001.12. |
| 69. | K. Asano, Y.Yamazaki, Y. Iijima, Hydriding and Dehydriding Behavior of LaNi5-xCox (x=0, 0.25, 2) Alloys, Proceedings of the Second International Symposium on New Protium Function in Materials , 97-100, 2001.06. |
| 70. | Y.Yamazaki, T. Nihei, J. Koike, T. Ohtsuki, Self-Diffusion of P in Pd-Cu-Ni-P metallic glass, Proceedings of the first international conference on diffusion in (DSL2005), 831-834, 2005.07. |
| 71. | A. Fujita, S. Fujieda, K. Fukamichi, Yoshihiro Yamazaki, Y. Iijima, Huge Volume Magnetostriction Controlled by Hydrogen Absorption in Itinerant-electron Metamagnetic La(FexSi1-x)13 Compounds, Trans. Mater. Res. Soc. Japan, 26, 219-222, 2001.01. |
| 72. | Y.Yamazaki, M. Sugihara, S. Takaki, K. Abiko, Y. Iijima, Volume and Grain-Boundary Self-Diffusion in a High-Purity Fe-50mass% Cr Alloy, Phys. Stat. Solidi a, 189, 1, 97-105, 2002.01. |
| 73. | Yoshihiro Yamazaki, O. Taguchi, T. Watanabe, Y. Iijima, Reaction Diffusion in the Au-Ti System between 1110K and 1150K, Defect Diff. Forum, 194, 1569-1574, 2001.04. |
| 74. | Yoshihiro Yamazaki, H. Kakuta, M. Okada, Y. Iijima, Interdiffusion in Au/Fe Couples under Elevated Hydrogen Pressures, Defect Diff. Forum, 194, 1069-1074, 2001.04. |
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