权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

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

氧化尖晶石的研究主要是因为其磁性。与氧尖晶石相比，硫磷尖晶石具有多种物理性质。我们成功地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。M-I跃迁的发现引起了国内外研究者的极大兴趣。这种新的硫尖晶石CuIr_2S_4在226 K发生了金属-绝缘体转变，这种金属-绝缘体转变伴随着从立方结构到四方结构的结构相变。CuIr_2S_4的高温金属相表现出Pauli顺磁性，低温绝缘相表现出反磁性，但由于芯电子的作用，反磁性贡献较大。观察到急剧的热容异常。测得相变的焓和熵分别为3.50kJ·mol ~（-1）<-1>和15.6J·<-1>mol ~（-1）。 ...更多信息 1、分别。CuIr_2S_4的电阻率在140 ~ 200 K之间表现为激活导电，激活能为4.7 × 10^2 eV，磁化率在228 K附近出现突变。然而，结构相变和M-I相变的起源和驱动力目前还不清楚。Jahn-Teller效应不能解释这些行为，但情况相当复杂。CuIr_2S_4的M-I转变机制至今仍是一个谜。众所周知，磁铁矿Fe_3O_4在119 K时发生相变（Verwey相变），并伴随着电导率的突变。本文指出了这种相变机制的可能性和相似性。目前正在进行进一步的详细研究，以澄清这些新现象。我们希望下面对CuIr_2（S_<1-x>，Se_x）_4体系的系统测量能对我们的讨论有所帮助。少