Experimental results on diffusion in alumina were summarized. The most reliable results were those for volume diffusion in single crystals (sapphire), and were available for a wide variety of substances, including O, Al, H2O, monovalent cations and trivalent cations. Experimental results on volume diffusion in polycrystalline alumina had also been reported for H, H2O, some actinides and rare earths. Diffusion coefficients were deduced from deep penetration tails on diffusion profiles, and were interpreted as resulting from fast diffusion along dislocations or grain boundaries. However, there were some uncertainties concerning these interpretations. The mechanisms of diffusion in alumina were also uncertain: various charged defects were suggested to control diffusion in alumina but no explanation was widely accepted because of discrepancies in the experimental results. The possibility of an AlO defect was advanced here in order to stimulate discussion. Taken together with a diffusion-reaction mechanism, it might explain many puzzling features of diffusion in alumina. The electrical conductivity of alumina resulted from the transport of H+(H3O+) ions if the OH concentration in the alumina was greater than about 3 x 10−7 OH groups per Al atom. At lower OH concentrations, electronic conductivity became dominant.

Diffusion in Alumina. R.H.Doremus: Journal of Applied Physics, 2006, 100[10], 101301 (17pp)