STUDIES ON THE CONDUCTION PROCESS OF CADMIUM-SUBSTITUTED COPPER CHROMITE SPINELS

Electrical resistivity (rho) and thermoelectric power (alpha) measurem ents were carried out in air on Cu1-xCdxCr2O4 (0 less-than-or-equal-to X less-than-or-equal-to 1.0) spinel oxides in the temperature ranges 300-873 K and 300-723 K, respectively. Thermal activation energy (E(a) ), carrier concentration (n), activation energy for carrier concentrat ion generation (E(n)), and mobility (mu) values have been calculated f rom the resistivity and thermoelectric power data. The results show th at conduction in cadmium-substituted CuCr2O4 samples is by hopping of charge carriers on the octahedral sites. The charge carrier hopping is , however, impeded at lower temperatures due to the larger C(oct)-Cr(o ct) distance when the large Cd2+ ion (97 pm) is substituted for the Cu 2+ ion (72 pm) in the tetrahedral site of the CuCr2O4 lattice. The tem perature dependence of alpha shows a change in the sign of the slope a t the temperature at which hopping conduction becomes evident. (C) 199 4 Academic Press, Inc.