Previous point-defect calculations for this material were used to rationalize O diffusion in undoped, MgO-doped and TiO2-doped samples. The amphoteric nature of the oxide was emphasized by the prediction that O and Al diffusion would be dominated by O vacancies and Al interstitials, or by O interstitials and Al vacancies; depending upon whether divalent or tetravalent impurities were present in greater abundance. The O diffusion data could be rationalized by using the calculated concentrations of O vacancies and O interstitials. The O vacancies appeared to be 2 to 2.5 times more mobile than O interstitials, whereas Al interstitials appeared to be 103 to 104 times more mobile than O vacancies. On the other hand, the calculations suggested that the migration energies of the O point defects were of the order of 4.5 to 5.9eV. It was not known whether these large values had any physical significance.

Oxygen Self-Diffusion in Corundum: a Conundrum. A.H.Heuer, K.P.D.Lagerlöf: Philosophical Magazine Letters, 1999, 79[8], 619-27