The self-diffusion of O in the monocrystalline garnet was measured by using the gas-solid isotope exchange technique, with 18O as a tracer, at 1060 to 1550C. The volume diffusion of O ions in the as-grown crystal could be described by:

D (m2/s) = 5.24 x 10-7 exp[-325(kJ/mol)/RT]

The coefficient depended upon the heat-treatment atmosphere prior to diffusion annealing. This effect upon O vacancy levels was attributed to the formation of an F-center-like defect and to the valency change of an Fe impurity. It was considered that this activation energy was due to O-ion migration. The O vacancy concentration of a faceted region of monocrystalline YAG was higher than in non-faceted regions.

Oxygen Diffusion in Single Crystal Yttrium Aluminum Garnet. H.Haneda, Y.Miyazawa, S.Shirasaki: Journal of Crystal Growth, 1984, 68[2], 581-8