Transport properties of Cu1−xZnxIr2S4 spinel compounds

Resistivity r and thermopower S of spinel compounds Cu1-xZnxIr2S4 with x < 0.3 have been measured at temperatures from 1.5 to 1000 K and under high pressures of up to 2 GP. The compounds undergo metal-insulator transition (MIT) at a temperature TMI which decreases with increasing x. In the low-temperature insulating phase, the resistivity of the compounds follows to the relation rexp(T*/T)1/2, suggesting Efros-Shklovskii variable range hopping conductivity mechanism. The inverse of the effective activation energy 1/T*, as it was obtained from r measured under hydrostatic pressure (P) for x=0, decreases linearly with P supporting the Efros-Shklovskii model. Thermopower S is positive in the insulating phase. It increases with temperature having a maximum somewhat below TMI, and abruptly decreases at TMI. In the metallic phase S is positive and linear in T up to at least 900 K. The maximum value of S in the insulating phase is about 4 times large for x=0.1 compared to x=0, and it quickly decreases with increasing x. The transport properties of CuIr2S4 are dependent on the sample preparation conditions. 10 refs.