Recent point-defect calculations for Al2O3 by Lagerlof and Grimes have been
used to rationalize oxygen diffusion in undoped, MgO-doped and TiO2-doped
Al2O3 The amphoteric nature of Al2O3 is emphasized by the calculations; oxy
gen and aluminium diffusion will be dominated by oxygen vacancies and alumi
nium interstitials, or oxygen interstitials or aluminium vacancies, dependi
ng on whether divalent or tetravalent impurities are present in greater abu
ndance. The oxygen diffusion data can be rationalized in a reasonably quant
itative manner by the calculated concentrations of oxygen vacancies and oxy
gen interstitials. Oxygen vacancies appear to be 2-2.5 times more mobile th
an oxygen interstitials, whereas aluminium interstitials appear to be 10(3)
to 10(4) times more mobile than oxygen vacancies. However, these calculati
ons suggest migration energies of the oxygen point defects of 4.5-5.9 eV. T
hese values are large, and it is not known whether they have any physical s
ignificance.