Self-diffusion and defect structure in cobaltous oxide

Abstract

The self-diffusion coefficients of cobalt in cobaltous oxide have been calculated from previously reported results of kinetics measurements of cobalt oxidation as a function of temperature and oxygen pressure. These results can be summarized by the following equation:

$$D_{Co} = const. \cdot {\text{p}}_{O_2 }^{{\text{1/n}}} \cdot exp ( - {\text{E}}_{\text{D}} /RT)$$

The activation energy of diffusion, E_D, increased with decreasing pressure, having values of 37 to 39.6 kcal/mole for oxygen pressures from 0.331 to 6.58×10⁻⁴ atm, respectively, whereas the exponent 1/n decreased from 1/3.3 to 1/3.95 as the temperature increased from 950 to 1300°C. It was found also that above 1050°C the defects of the cation sublattice resulting from nonstoichiometry and the intrinsic Frenkel disorder overlap. Thus, at temperatures higher than 1050°C the deviations from stoichiometry cannot be regarded as an adequate measure of the concentration of point defects in cobaltous oxide.