Oxygen Grain Boundary Diffusion in Alumina, Impurity Effects

Oxygen self-diffusion measurements were performed both in unintentionally doped Al sub 2 O sub 3 ceramics and in oriented single crystals. The tracer exp 18 O was introduced by solid/gas isotropic exchange. The diffusion profiles were determined by secondary ion mass spectrometry. In the single crystals, the evidence of short-circuit effects led to consider a diffusion contribution of the dislocation walls existing in the samples. Volume and subboundary diffusion coefficients were determined. They are characterized by activation enthalpies of, respectively, 636 and 896 kJ/mol. A series of experiments on polycrystalline material (obtained by sintering alumina powder of the same origin than the single crystals) gave an activation enthalpy for grain boundary diffusion of 921 kJ/mol, again higher than the volume diffusion one. This unusual result can be explained by considering the effect of impurity segregation on the grain boundary self-diffusion.