Self-diffusion in α‒Al₂O. IV. Oxygen grain-boundary self-diffusion in undoped and yttria-doped alumina polycrystals

Abstract

Oxygen self-diffusion coefficients were determined in polycrystals of α-alumina either ‘undoped’ or doped with 500wt.ppm (225molppm) Y₂O₃ in the temperature range 1460-1720°C, with ¹⁸O₂ and secondary-ion mass spectrometry. Oxygen grain-boundary diffusion coefficients obey the relations

for ‘undoped’ alumina and

for ‘yttrium-doped’ alumina.

The comparison between the two materials indicates that yttrium addition decreases the oxygen grain-boundary diffusion. For both materials, it was observed that the activation energy of grain-boundary diffusion is greater than the activation energy of the bulk diffusion. Similar results were obtained in single crystals for diffusion in the bulk and in subboundaries. These results were interpreted as being due to impurity segregation along boundaries and led to a model.