Electrical conductivity data for undoped monocrystalline and polycrystalline materials were explained in terms of a defect disorder model which was based upon the assumption that doubly-ionized Co vacancies were the predominant defects. An analysis which was based upon the Debye-Hückel theory for liquid electrolytes was used to evaluate interactions between defects such as doubly-ionized cation vacancies. It was shown that, at temperatures ranging from 1200 to 1700K, the reciprocal of the power-law exponent for the O partial pressure dependence of the electrical conductivity varied from 3.5 to 3.8. At about 1300K, this exponent was higher for monocrystalline than for polycrystalline specimens. It was shown that a closer agreement between the defect model and experimental data could be obtained by using defect activities instead of concentrations.

G.Borchardt, K.Kowalski, J.Nowotny, M.Rekas, W.Weppner: Journal of Materials Science, 1996, 31[19], 5185-90