| Project/Area Number |
09640485
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
物理学一般
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| Research Institution | HIROSHIMA UNIVERSITY |
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Principal Investigator |
INUI Masanori Hiroshima University, Faculty of Integrated Arts and Sciences, Assistant Professor, 総合科学部, 助教授 (40213136)
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| Co-Investigator(Kenkyū-buntansha) |
TAMURA Kozaburo Hiroshima University, Faculty of Integrated Arts and Sciences, Professor, 総合科学部, 教授 (30155262)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1998: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1997: ¥2,700,000 (Direct Cost: ¥2,700,000)
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| Keywords | semiconductor / metal / supercritical tluid / small angle x-ray scattering / x-ray diffraction / x-ray absorption / high temperature / high pressure / X線回析 / 密度揺らぎ / 相関距離 |
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| Research Abstract |
Liquid Se has two-fold coordinated chain structure at normal pressure and has semi conducting properties. As the volume is expanded with increasing temperature and pressure, fluid (f-) Se undergoes a semiconductor-metal (SC-M) transition in the supercritical region. With further volume-expansion, the metallic fluid becomes insulating vapor consisting of Se dimers. It is interesting to study how the Se dimers in the vapor condense to be the metallic fluid. Large fluctuations are expected to affect the condensation process. We have carried out small angle x-ray scattering (SAXS) and x-ray absorption fine structure (XAFS) measurements for supercritical fluid Se near the critical point (critical temperature ; 1615ﾟC, critical pressure ; 385bar) to study the correlation between the local structure and density fluctuations. XAFS measurements were carried out using synchrotron radiation at the European Synchrotron Radiation Facility. XAFS spectra for insulating Se vapor were obtained at l65OﾟC and at pressures up to 600bar. The results show that the vapor with smaller density than the critical density consists mainly of Se dimers arid that with larger density than the critical density consists of the dimers and chain molecules. The SAXS measurements were carried out using in-house x-ray source at Hiroshima University and we have observed the critical opalescence of f-Se for the first time. Using the SAXS intensity of a high pressure He gas as a reference, we have obtained the absolute values of the SAXS intensity of f-Se. The correlation length of about 20A and the density fluctuation of about 15 are deduced from the observed spectra near the critical density using Orenstein-Zernike formula. The obtained density fluctuation strongly suggests that Se dimers in the dense region induced by the fluctuation form chain molecules. The mixture of the dimers and chain molecules observed by the XAFS spectroscopy is considered to come from such density fluctuations.
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