Hopping Conductivity in CuIr_2S_4 Spinel Compound : I. Empirical Model for Electronic Configuration and Mechanism of Metal-Insulator Transition(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

概要

論文の詳細を見る
Two types of spinel compound CuIr_2S_4 samples were investigated: sample 1 was synthesized under protective Ar atmosphere to avoid contamination by oxygen, whereas sample 2 was exposed to oxygen during preparation procedure. According to the results of scanning electron microscopy, the oxygen concentration in sample 2 is 5 times higher than in sample 1. However, the metal-insulator transition (MIT) temperature is the same for both samples irrespective of oxygen concentration. The conductivity σin the insulating phase (LIP) is proportional to exp[numerical formula] at T≤120K for sample 1 and at T≤50K for sample 2, while in the metallic phase the resistivity p is proportional to the same function of σ in LIP for both samples. Temperature independent diamagnetic susceptibility and temperature dependence of thermopower suggest that this compound is not a normal activation-type semiconductor. The electronic configuration of CuIr_2S_4 is estimated to a first approximation from the experimental results. 5dε electrons do not participate in the crystallization bonds of dγ^2s^1p^3 for spinel structure, however these electrons are responsible for MIT and for conductivity. The cooperative Jahn-Teller effect with dimerization is proposed for MIT: The energy of an electronic system of 5dε decreases at the expense of crystallographic energy coming from the dγ^2s^1p^3 electron system due to tetragonal deformation as in normal Jahn-Teller effect. Further triclinic deformation occurs to minimize energy by dimerization of 5dε(xy) orbitals in the <110> direction, resulting in charge ordered Pierls state. A new type of conductivity named traveling dimer conduction is proposed.
社団法人日本物理学会の論文
2006-07-15

Hopping Conductivity in CuIr_2S_4 Spinel Compound : I. Empirical Model for Electronic Configuration and Mechanism of Metal-Insulator Transition(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

スポンサーリンク

概要

著者

関連論文

スポンサーリンク