The Crystal Structures in Hydrogen Absorption Reactions of REMgNi4-Based Alloys (RE: Rare-Earth Metals)

REMgNi4-based alloys, RE(2−x)MgxNi4 (RE: rare-earth metals; 0 < x < 2), with a AuBe5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2−x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2−x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2−x)MgxNi4

The Crystal Structures in Hydrogen Absorption Reactions of REMgNi₄-Based Alloys (RE: Rare-Earth Metals)

REMgNi4-based alloys, RE(2−x)MgxNi4 (RE: rare-earth metals; 0 5-type crystal structure, exhibit reversible hydrogen absorption and desorption reactions, which are known as hydrogen storage properties. These reactions involve formation of three hydride phases. The hydride formation pressures and hydrogen storage capacities are related to the radii of the RE(2−x)MgxNi4, which in turn are dependent on the radii and compositional ratios of the RE and Mg atoms. The crystal structures formed during hydrogen absorption reactions are the key to understanding the hydrogen storage properties of RE(2−x)MgxNi4. Therefore, in this review, we provide an overview of the crystal structures in the hydrogen absorption reactions focusing on RE(2−x)MgxNi4

Crystal Structural Determination of SrAlD5 with Corner-Sharing AlD6 Octahedron Chains by X-ray and Neutron Diffraction

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Pressure–Temperature Phase Diagram of Ta-H System up to 9 GPa and 600 °C

室温で5 GPa以上の水素雰囲気下での加圧によりTaHからTaH2が生成することが近年報告された。高温高圧下での相関係が未報告であり、本研究では放射光その場観察によりTa-H系の相関係を決定した。得られた結果はTaを含む新規水素化物の合成に有用な知見となる

Depressurization-induced diffusionless transformation in pure iron hydrogenated under several gigapascals

8.6 GPa、室温でdhcp構造をとっていたFeHを減圧したところ、徐々にbcc 相に構造相転移した。走査電子顕微鏡観察の結果、この構造相転移は無拡散型の相転移であることが分かった。bcc相はラス微細構造を示し、1.9 GPaでの保持で成長することから、この相転移が水素の拡散や放出を必要とするベイナイト変態であると考えられる

High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations

The high-pressure structural behavior of the binary intermetallic compounds CoSn, FeSn, and NiIn with the peculiar void containing CoSn (B35)-type structure has been studied by means of room-temperature diamond anvil cell and high-temperature multianvil experiments, as well as by first-principles calculations. All three compounds remain structurally stable at pressures up to at least 25 GPa, whereas first-principles calculations predict high-pressure structural changes below 20 GPa. A plausible explanation for the discrepancy is that at room temperature, a sizable activation barrier inhibits kinetically the transformation into more close-packed polymorphs. It is supported by our experiments at temperatures around 1000 °C and a pressure of 10 GPa. At these conditions, NiIn transforms into the temperature-quenchable stoichiometric CsCl-type high-pressure phase, which has been predicted in our first-principles calculations. However, CoSn and FeSn decompose into a mixture of compounds richer and poorer in tin, respectively. Nevertheless, it might be possible that lower temperatures and higher pressures may afford theoretically predicted polymorphs. In particular, a phase transformation to the FeSi-type structure predicted for CoSn is of interest as materials with the FeSi-type structure are known for unusual thermal and transport properties.Original publication: Mikhaylushkin, A.S., Sato, T., Carlson, S., Simak, S.I., and Häussermann, U., High-pressure structural behavior of large-void CoSn-type intermetallics: Experiments and first-principles calculations, 2008, Physical Review B, (77), 014102. http://dx.doi.org/10.1103/PhysRevB.77.014102. Copyright: American Physical Society, http://publish.aps.org

Hydrogenation treatment under several gigapascals assists diffusionless transformation in a face-centered cubic steel

準安定fcc相の鉄鋼材料に数GPaの高圧水素化処理を施すことにより、細かなラス構造のbcc相を回収することに成功した。高圧下で水素化反応が、脱圧過程で水素放出が起きるが、後者で進行する無拡散相変態によって上記構造が実現することが分かった。高圧水素化と脱水素化を利用した新しい微細組織制御技術の実現につながる成果である

Depressurization-induced diffusionless transformation in pure iron hydrogenated under several gigapascals

Phase transformation in hydrogenated iron during depressurization from several gigapascals was investigated through in-situ synchrotron radiation X-ray diffraction and post-mortem electron backscatter diffraction measurements. The hydrogenated iron under 8.6 GPa at 293 K showed a double hexagonal close-packed (dhcp) structure, and it gradually transformed into a body-centered cubic (bcc) structure with decreasing pressure. The final crystal structure consisted entirely of a bcc phase. The structural change from dhcp to bcc structure was diffusionless-type phase transformation. The bcc phase showed lath morphology and could grow during aging under a constant pressure of 1.9 GPa, which indicated that it was bainitic-type transformation that required hydrogen diffusion or desorption