Metal-Insulator Transition in Cu Spinel Compounds Originated from the Jahn-Teller Effect

铜尖晶石化合物中源自 Jahn-Teller 效应的金属-绝缘体转变

基本信息

批准号：
06640461
负责人：
NAGATA Shoichi
金额：
$ 1.34万
依托单位：
Muroran Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

The oxyspinels have been extensively studied mainly for the magnetic properties. In contrast to the oxyspinels sulphospinels exhibit the wide variety of physical properties. We have synthesized successfully a new spinel-type compound CuIr_2S_4 and discovered a metal-insulator (M-I) transition. After this discovery of M-I transition, many researchers are stronglyinterested in this new compounds all over the world. This new thiospinel CuIr_2S_4 exhibits a metal-insulator transition at 226K.This metal-insulator transition is associated with astructural phase transition from a cubic to a tetragonal structure with decreasing temperature. The high-temperature metallic phase of CuIr_2S_4 reveals Pauli paramagnetism and the lower-temperature insulating phase has semiconductive behavior with a rather large diamagnetic contribution due to the core electrons. A sharp heat capacity anomaly is observed. The enthalpy and entropy of the transition are found to be 3.50kJmol^<-1> and 15.6JK^<-1> mol^<- … More 1>, respectively. The electrical resistivity in CuIr_2S_4 shows activated conduction with an activation energy of 4.7*10^2 eV between 140 and 200K.The magnetic susceptibility exhibits a sharp change near 228K.There has been a lot of investigation for the M-I transition in CuIr_2S_4. However, the origin and the driving force for the structural phase transition and the M-I transition is not understood at the present time. The Jahn-Teller effect can not explain these behavior, but the situation is rather complicated. The mechanism of the M-I transition in CuIr_2S_4 remains enigmatic, which must be solved. It is well known that magnetite Fe_3O_4 undergoes a phase transition (the Verwey transition) accompanied by a sudden change of conductivity at 119K.A possibility and the analogy for the mechanism in the M-I transition has been pointed out. Further detailed study to clarify the novel phenomena is currently under way. It is our hope that the systematic measurements presented below for the system of CuIr_2 (S_<1-x>, Se_x)_4 will be helpful and lead to the fruitful discussion. Less

与氧尖晶石相比，硫尖晶石表现出多种物理性质，我们已成功合成了一种新的尖晶石型化合物 CuIr_2S_4，并发现了金属-绝缘体（M-I）转变。随着M-I转变的发现，世界各地的许多研究人员都对这种新的化合物产生了浓厚的兴趣。这种新的硫尖晶石CuIr_2S_4表现出一种226K 时发生金属-绝缘体转变。这种金属-绝缘体转变与随温度降低从立方结构到四方结构的结构相变有关。CuIr_2S_4 的高温金属相显示出泡利顺磁性，而低温绝缘相具有半导体行为。由于核心电子的反磁性贡献相当大，观察到了明显的热容异常。 CuIr_2S_4 的电阻率分别为 3.50kJmol^<-1> 和 15.6JK^<-1> mol^<- … More 1>，在 140 和 140 之间表现出活化能为 4.7*10^2 eV 的活化传导。 200K。磁化率在228K附近表现出急剧变化。对于M-I转变已经有很多研究。 CuIr_2S_4。目前尚不清楚结构相变和M-I转变的起源和驱动力，Jahn-Teller效应无法解释这些行为，但M-I的机制相当复杂。 CuIr_2S_4 中的转变仍然是个谜，必须解决这个问题。众所周知，磁铁矿 Fe_3O_4 在119K. 已经指出了 M-I 转变机制的可能性和类比，目前正在进行进一步详细研究以阐明新现象。我们希望下面对 CuIr_2 (S_< 系统) 进行系统测量。 1-x>, Se_x)_4 将很有帮助并带来富有成果的讨论。