The electrical conductivity of CoO: Experimental results and a new conductivity model

Abstract

Abstract The electrical conductivity of the transition metal oxide Co 1 ‐σO has been measured as a function of the oxygen activity and the temperature in the whole stability field of CoO using a very pure single crystal. The results are modelled in terms of a new conductivity model in which free electron holes as well as electron holes which are trapped by cation vacancies contribute to the conductivity. At low oxygen activities also electrons are considered. Within this model the following parameters are obtained: the two mass action constants, K 1 and K 11 , for the incorporation of oxygen and the formation of singly ionized vacancies, the mobilities of free and trapped electron holes, b 0 and b 1 , and the product of the electron mobility and the electronic mass action constant, K e b e . A microscopic interpretation of the model is made possible by translating the so‐called five‐frequency model for impurity diffusion to the conductivity problem. Then it is also possible to estimate the lifetime of the associate consisting of a doubly ionized vacancy and an electron hole, which is about twenty times larger than the residence time of an electron hole on a cation site.