Oxygen Ion Diffusion in Single‐Crystal and PoIycrystaIIine Yttrium Iron Garnet

The oxygen ion self‐diffusion coefficient was determined for single‐crystal and polycrystalline yttrium iron garnet (Y 3 Fe 5 O 12 ). The rate of exchange between oxygen gas enriched with the stable isotope 18 O and solid yttrium iron garnet was measured. Oxygen ion diffusion rates were found to be the same in single‐crystal and 8μ polycrystalline Y 3 Fe 5 O 12 between 1100° and 1400°C. This is in contrast to previous measurements of anion diffusion in several alkali halides and in AI 2 O 3 where a strong dependence of diffusion rates on the presence of grain boundaries was found. Enhancing oxidation rates in dense, reduced yttrium iron garnet at low temperature by minimizing the final fired grain size in the sintering process does not appear to be possible on the basis of the results obtained in this investigation. The temperature dependence of the diffusion coefficient of oxygen measured at 100 torr can be represented by D = 0.40 exp (‐65.4/RT) cm 2 per second.