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An X-ray Study on Pressure Phase Transition and Electron Distribution of Transition Metal Chalcogenides.

过渡金属硫属化物压力相变和电子分布的 X 射线研究。

基本信息

批准号：
01470056
负责人：
MARUMO Fumiyuki
金额：
$ 0.51万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

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.

用单晶X射线衍射方法研究了黄铁矿型NiS_2和NiSe_2晶体在高压下的结构和电子分布变化。NiS_2在常压下为半导体，在46 kbar左右转变为金属导电，而NiSe_2没有这种相变。NiS_2的晶胞尺寸a在相变压力下呈不连续变化，a（A）在低于相变点的压力范围内近似为p（kbar）a=5.6881-0.00198p，从相变点到90 kbar的压力范围内近似为a=5.6650-0.00171p。NiSe_2的尺寸a在60 kdar以内也呈线性变化，近似关系为a=5.9605-0.00219p。在NiS_2上得到的结果与本研究者在用与本研究中所用的晶体合成方法不同的方法制备的NiS_2晶体上得到的结果不一致。这一事实表明，从化学计量组成的一个小的差异很大程度上影响相变压力的可能性。键距的压力依赖性在Ni-Se中最大，在Se-Se-中最小。NiS_2中Ni^<2+>离子周围的电子分布具有八面体场中3d^8离子的特征。在高于转变点的高压下，电子分布具有与1巴时相似的特征。然而，差分傅立叶映射表明，3d电子的分布在高压下比在1巴下稍微扩大。