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Pressure-induced phase transitions of transition metal chalcogenids.

压力诱导的过渡金属硫族化合物的相变。

基本信息

批准号：
12640331
负责人：
KOBAYASHI Hisao
金额：
$ 2.24万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

The electronic states of 3d transition-metal compounds where an electron correlation plays an important role, have been interesting subjects. One of the interesting properties in these compounds is an insulator-metal transition. Since FeS is an antiferromagnetic semiconductor, it is a good candidate to study a pressure induced insulator-metal transition and of interest to condensed matter physics as well as planetary science. As indicated by the high-pressure x-ray diffraction measurements, FeS undergoes two first-order structural phase transitions at 3.5 and 6.5 GPa. Recently we have measured the electrical resistivity under high pressure. It was found that the semiconductor-metal-semiconductor transitions occur in FeS under pressure up to 8 GPa. In these phase transitions, not only the electron correlation but also an electron phonon coupling plays an important role. We have measured inelastic nuclear resonate scattering of FeS under high pressure to obtain the pressure dependence of phonon densities.The nuclear resonant inelastic x-ray scattering were measured by tuning the highly monochromatzed beam in a range of about 80meV on 3-ID beamline at APS, Argonne National Laboratory using a special DAC. The use of Fluorinert as pressure-transmitting medium ensured quasihydrostatic conditions. Pressure was obtained by the ruby calibration.The observed nuclear resonant inelastic scattering spectra consist of a center peak originating from elastic scattering and sidebands resulting from inelastic scattering with annihilation and creation of phonon. Almost all-vibrational modes are observed in a energy range up to 60meV. The partial phonon densities of states of FeS in each phase were extracted from these spectra assuming a harmonic lattice model. The observed changes in the phonon densities of states in FeS under pressure reflect the structural phase transitions.

三维过渡金属化合物的电子态是一个有趣的研究课题，其中电子相关起着重要的作用。这些化合物中一个有趣的特性是绝缘体-金属的转变。由于FeS是一种反铁磁半导体，它是研究压力诱导绝缘体-金属转变的良好候选者，并且对凝聚态物理和行星科学感兴趣。高压x射线衍射测量表明，FeS在3.5和6.5 GPa时经历了两次一级结构相变。最近我们测量了高压下的电阻率。结果表明，在高达8gpa的压力下，FeS发生了半导体-金属-半导体转变。在这些相变中，除了电子相关外，电子声子耦合也起着重要作用。我们在高压下测量了FeS的非弹性核共振散射，以获得声子密度的压力依赖性。在美国阿贡国家实验室（APS）的3-ID束流线上，利用专用DAC对高度单色光束在约80meV范围内进行调谐，测量了核共振非弹性x射线散射。氟化物作为传压介质的使用保证了准流体静力条件。通过红宝石校准获得压力。观测到的核共振非弹性散射谱由弹性散射产生的中心峰和湮灭和声子产生的非弹性散射产生的边带组成。几乎所有的振动模式都在60meV的能量范围内被观察到。采用谐波晶格模型，从这些谱中提取了FeS各相态的部分声子密度。在压力作用下，FeS中声子密度的变化反映了结构相变。