Deviations from Local Thermodynamic Equilibrium During Interdiffusion of CoOMgO and CoONiO

Abstract

Abstract The assumption of local thermodynamic equilibrium during interdiffusion between CoO and MgO and between CoO and NiO at a given oxygen potential of the ambient atmosphere is discussed. Although the oxygen anions are virtually immobile, macroscopic markers (pores, Pt) move toward the CoO‐rich end of the metal‐deficient semiconducting oxide during interdiffusion. It is shown independently that the markers move under the action of an oxygen potential gradient opposite to the vacancy flux. The existence of a gradient in the oxygen potential in the diffusion zone shows that local equilibrium is not established. It is found that the deviations from local equilibrium do not, within the range of experimental uncertainty, result in time‐dependent interdiffusion coefficients.