Small-polaron mobility in nonstoichiometric cerium dioxide

Abstract

The high temperature drift mobility ([mu]d) of charge carriers in nonstoichiometric cerium dioxide (CeO2-x) has been calculated by combining the electrical conductivity and nonstoichiometry data on the basis of the oxygen vacancy model with correct ionization state. The electrical conductivity was measured by a four-probe d.c. technique and the nonstoichiometry by thermogravimetric analysis. The dilute solution model of the point defects is valid up to x = 0.03. From the magnitude of [mu]d and its temperature dependence, the charge carriers in CeO2-x, are proposed to be small-polarons formed by localization of electrons at cerium sites and the charge transport process is proposed to occur by a hopping mechanism. The observed temperature dependence of [mu]d is in accord with that derived by Holstein and Friedman for small-polaron transport by the hopping mechanism. The activation energy of mobility is found to increase with increasing x as expected for the hopping model.