Metal-insulator transition and superconductivity in spinel-type system Cu1-xZnxIr2S4

The thiospinel compound CuIr2S4 exhibits the metal-insulator (M-I) transiti on accompanied by the structural transition. In this work, compounds of Cu1 -xZnxIr2S4 in the composition range 0 less than or equal to x less than or equal to 0.5 were synthesized to examine the effects of excess electrons su pplied by replacing Cu with Zn. The samples mere investigated by measuremen ts of X-ray diffraction, electrical resistance and magnetic susceptibility. The hd-l transition temperature T-MI decreases with increasing a:. Results are discussed on the basis of the model of charge ordering for the insulat ing state. It was found that the samples with a: greater than or equal to 0 .3 show no M-I transition and exhibit superconductivity. The transition tem perature T-C is 2.8K for a: = 0.3 and 2.2K for x = 0.5. The ground state of the system changes from insulating to superconducting with increasing Zn c ontent.