| Project/Area Number |
01470056
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
MARUMO Fumiyuki Tokyo Institute of Technology, Research Laboratory of Engineering Materials, Professor, 工業材料研究所, 教授 (10013492)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIZAWA Nobuo Tokyo Institute of Technology, Research Laboratory of Engineering Materials, Ass, 工業材料研究所, 助教授 (90151365)
TANAKA Kiyoaki Nagoya Institute of Technology, Faculty of Engineering Associate Professor, 工学部, 助教授 (00092560)
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| Project Period (FY) |
1989 – 1990
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1990: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | electron distribution / X-ray diffraction / high pressure / phase transition / difference Fourier map / 3d electron / pyrite-type / 差フ-リェ合成図 / 二硫化ニッケル / ニセレン化ニッケル / モット転移 / 超高圧 / 黄鉄鉱型構造 |
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| Research Abstract |
Changes of structures and electron distributions were investigated on pyrite-type crystals of NiS_2 and NiSe_2 under high pressure by means of the single-crystal X-ray diffraction method. NiS_2 is a semiconductor under ambient pressure and transformed to show metallic conduction at about 46kbar, whereas NiSe_2 shows no such a phase transition. The cell dimension a of NiS_2 changes discontinuously at the phase transition pressure, and a (A) is approximated with a linear formula of p (kbar) a=5.6881-0.00198p in the pressure region lower than the transition point and a=5.6650-0.00171p from the transition point to 90 kbar. The dimension a of NiSe_2 also changes linearly up to 60 kdar and is approximated with the relation a=5.9605-0.00219p. The result obtained on NiS_2 is inconsistent with that obtained by the present investigators on a NiS_2 crystal prepared by a different method from that employed to synthesize the crystal used in the present investigation. The fact suggests the possibility that a small discrepancy from the stoichiometric composition largely affects the phase transition pressure. The pressure dependence of bond distances is largest in Ni-Se and smallest in Se-Se-. The Ni-S distance changes discontinuously at the transition pressure and the pressure dependence becomes lower above the transition point.
The electron distribution around the Ni^<2+> ion in NiS_2 showed a feature characteristic to 3d^8 ions in octahedral fields. Under high pressure above the transition point, electron distribution has a similar feature as that at 1 bar. However, the difference Fourier maps indicated that the distribution of 3d electrons a little more expands under high pressure than at 1 bar.
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