Study of the pressure-induced phase transition on molecular conductors from the X-ray diffraction measurement

本研究的目的是发展分子导体的高压结构研究。采用“易操作”的粉末X射线衍射型金刚石对顶砧装置研究了高压结构，发现具有极一维电子体系的分子导体Me_4X（CPDT-TCNQ）_2（X=N，P，As）在135 K（X=N），165 K（X=P）和185 K（X=As）出现金属-绝缘体转变。低温下的转变起因与阳离子的置换不同。对于Me_4N、Me_4P、Me_4As化合物，在室温加压下也观察到了绝缘态。通过高压X射线衍射测量，确定了Me_4N、Me_4P盐的高压相变是由2_kFCDW引起的，Me_4As盐的高压相变是由4kFCDW引起的。我成功地完成了这一系列化合物的普适压力-温度相图。一维π-d导体（DBr-DCNQI）_2Cu和（DI-DCNQI）_2Cu的导电性质随Cu原子的电子态而发生剧烈变化。晶格参数的详细研究阐明了高压反常金属相结构的显著差异。这种结构特征是两种化合物出现不同高压金属态的原因。这一结果将有助于对具有独特的压力下电磁性质的DCNQI系统的研究。

The intention of this research is to develop the high-pressure structural study for molecular conductors. The "easy handling" powder X-ray diffraction type diamond anvil cell was produced to study the high-pressure structure investigation.Molecular conductors Me_4X(CPDT-TCNQ)_2 (X=N, P, As) having the extremely one-dimensional electronic system show the metal-insulator transition at 135K (X=N), 165K (X=P) and 185K (X=As). The origin of the transition at low temperature is different with the displacement of the cation. For Me_4N, Me_4P, Me_4As compounds, the insulating states were also observed under pressure at room temperature. From the high-pressure X-ray difrraction measurement, I identified that the transitions under pressure are originated by the 2_kF CDW for Me_4N, Me_4P salts and 4k_FCDW for Me_4As salt. I succeeded to complete the universal pressure-temperature phase diagram for the series of the compounds. The present result is significant to the research for a variety of one-dimensional molecular conductors.One-dimensional π-d conductors (DBr-DCNQI)_2Cu and (DI-DCNQI)_2Cu show drastic changes in the conducting properties depending on the electronic state of Cu atoms. The detail investigation of the lattice parameter clarifies the sight difference of their structures in the high-pressure anomalous metallic phases. This structural character is the origin of the appearance of the different high-pressure metallic state for the both compounds. This result would contribute the development of the research for the DCNQI system having the unique electronic and magnetic properties under pressure.