| 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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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥50,180,000 (Direct Cost: ¥38,600,000、Indirect Cost: ¥11,580,000)
Fiscal Year 2007: ¥12,350,000 (Direct Cost: ¥9,500,000、Indirect Cost: ¥2,850,000)
Fiscal Year 2006: ¥13,260,000 (Direct Cost: ¥10,200,000、Indirect Cost: ¥3,060,000)
Fiscal Year 2005: ¥24,570,000 (Direct Cost: ¥18,900,000、Indirect Cost: ¥5,670,000)
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| Keywords | rare-earth metal / hydride / structural transition / electronic transition / high pressure / 金属転移 / 高圧 / 金属水素化物 / 圧力誘起相転移 |
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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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