2007 Fiscal Year Final Research Report Summary
Synthesis of Metal Hydrides using Densified Hydrogen Fluid and Clarification of The Electronic transition Mechanism
| Project/Area Number |
17204032
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Condensed matter physics II
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| Research Institution | Japan Atomic Energy Agency |
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Principal Investigator |
AOKI Katsutoshi Japan Atomic Energy Agency, Quantum Beam Science Directorate, Supreme Researcher (30356331)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEMURA Kenichi National Institute for Materials Science, Advanced Nano Materials Research Center, Chief Researcher (20171671)
SHIMIZU Katsuya Osaka University, Center for Quantum Science and technology under Extreme Conditions, Professor (70283736)
SHIMIZU Hiroyasu Gifu University, Faculty of Engineering, Professor (80023258)
SHINJI Tsuneyuki University of Tokyo, Faculty of Science, Professor (90197749)
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| Project Period (FY) |
2005 – 2007
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| Keywords | rare-earth metal / hydride / structural transition / electronic transition / high pressure |
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| Research Abstract |
The structural and electronic transitions have been studied for rare-earth metal hydrides highly pressurized in a region of several tens of gigapascals. The sequential structural transition from a hexagonal to fcc lattice via an intermediate long-period stacking structure was establish by the x-ray diffraction measurements systematically made for ScH_3, YH_3 and LaH_3 and the onset pressures of hexagonal-fcc transition were shown to be inversely proportional to the ionic radius of the tri-hydride metals. The is metal seemed to be realized in fcc YH_3 at pressures around 23GPa. The band gap closure was confirmed experimentally by optical absorption measurement in infrared region and theoretically by a band structure calculation. No signal of super conducting transition was detected at low temperatures down to10K, however.
The long-period stacking structure of YH_3, which appeared as an intermediate structure bridging the low-pressure hexagonal and high-pressure fcc structures, showed a rapid decrease in band gap energy. This was likely due to the displacement of the hydrogen atoms initially located near the metal planes toward the central symmetric positions in the octahedral interstitial sights. The band gap energy has theoretically been shown to depend on the hybridization state between the hydrogen is and yttrium 4d or the locations of the hydrogen positions in the octahedral sites. The softening and weakening of the hydrogen vibrational peaks measured by Raman scattering and infrared absorption measurements indicated the gradual displacement of the hydrogen atoms toward the symmetric center as expected from the theoretical results. Photochromism observed for the coexistence state of fcc-YH_2 and hexagonal-YH_3 suggested that the hydrogen atoms would transfer between the sites to form the bonding states site-dependently. These phenomena were characteristic to metal hydride and indicative of the importance of further dynamics study of hydrogen-metal system.
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[Presentation] YH_2の圧力誘起分解現象2007
Author(s)
町田晃彦、綿貫徹、大村彩子、青木勝敏
Organizer
第48回高圧討論会
Place of Presentation
倉吉パークスクエア、鳥取
Year and Date
20071100
Description
「研究成果報告書概要(和文)」より
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[Presentation] YH_3の圧力誘起構造変化2006
Author(s)
町田晃彦,大村彩子,綿貫徹,青木勝敏,竹村謙一
Organizer
第47回高圧討論会
Place of Presentation
熊本市産業文化会館(熊本)
Year and Date
20061100
Description
「研究成果報告書概要(和文)」より
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[Presentation] 希土類金属水素化物の電子転移2005
Author(s)
青木勝敏,町田晃彦,大村彩子,綿貫徹,中野智志,竹村謙一
Organizer
物性研短期研究会:固体における水素の科学
Place of Presentation
東京大学物性研究所(柏)
Year and Date
20051100
Description
「研究成果報告書概要(和文)」より
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[Presentation] Y水素化物の高圧赤外分光2004
Author(s)
大村彩子,町田晃彦,綿貫徹,青木勝敏,中野智志,竹村謙一
Organizer
第45回高圧討論会
Place of Presentation
立命館大学(びわこ・くさつ)
Year and Date
20041000
Description
「研究成果報告書概要(和文)」より
