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

氧尖晶石被广泛的研究主要是因为它的磁性。与氧尖晶石相比，硫尖晶石表现出各种各样的物理性质。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。自从M-I转变被发现后，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在226K出现金属-绝缘体相变，这种金属-绝缘体相变与立方结构到四方结构的相变有关。CuIr_2S_4的高温金属相表现出泡利顺磁性，而低温绝缘相由于核电子的存在而具有较大的抗磁贡献的半导体行为。观测到了明显的热容异常。相变的焓和熵分别为3.50kJmol^-1和15.6kJmol^-1-…分别增加了1&>1家。CuIr_2S_4的电阻率在140~200K之间表现为激活电导，激活能为4.7×10~(-2)eV。磁化率在228K附近发生急剧变化。关于CuIR_2S_4的M-I相变已有大量研究，但结构相变和M-I相变的起源和驱动力目前尚不清楚。Jahn-Teller效应无法解释这些行为，但情况相当复杂。CuIr_2S_4的M-I转变机制仍然是个谜，必须解决。众所周知，磁铁矿Fe_3O_4在119K经历了伴随电导率突变的相变(Verwey相变)，并对M-I相变的机理进行了类比。目前正在进行进一步的详细研究，以澄清这些新现象。我们希望下面给出的CuIr_2(S；1-x&gt；，Se_x)_4体系的系统测量结果将有所帮助，并导致富有成效的讨论。较少

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