Self-Diffusion of Oxygen in Single Crystal and Polycrystalline Aluminum Oxide

The self-diffusion coefficient of oxygen has been determined as a function of temperature in single crystal and polycrystalline aluminum oxide at temperatures up to 1780°C. The rate of exchange between a gas phase and solid particles was measured, utilizing the stable isotope, O18. In single crystals of aluminum oxide intrinsic diffusion occurs in a high temperature region, depending on temperature as D=1.9×103 exp (—152 000/RT). At temperatures below about 1600°C variable results were obtained depending on impurity content and previous heat treatment. For one set of samples experimental results could be represented as D=6.3×10—8 exp (—57 600/RT). The diffusion coefficient of oxygen in polycrystalline samples is about two orders of magnitude larger than that found for the single crystals, and has a somewhat smaller activation energy. With the polycrystalline oxide, variable results were also observed at lower temperatures.