ELECTRICAL-CONDUCTIVITY AND THERMOPOWER OF GA1-XZNXV4S8

V-4-cluster compounds Ga1-xZnxV4S8 (x = 0-0.1) have been prepared by d ifferent heat treatments. The transport properties are strongly sensit ive to the short-range order of <F(4)over bar 3m> <-> Fd3m variety, th e high temperature disordered phases being more insulating. The increa sed Zn-substitution of Ga gave homogeneous phases of <F(4)over bar 3m> symmetry and strong reduction in room temperature activation energy i n conductivity from 0.14 to 0.04 eV in 10% Zn compound. The thermopowe r is predominantly p-type and nearly temperature independent for Zn su bstituted compounds. These properties are discussed in terms of hoppin g of carriers in a Mott insulator in the presence of disorder.