Self-diffusion of yttrium in monocrystalline yttrium oxide: Y 2O 3

Abstract

Yttrium self-diffusion in monocrystalline yttrium oxide (Y 2O 3) is studied by means of the classical radio tracer technique. The few reliable diffusion data obtained in the temperature range 1600–1700°C lead to the following diffusion coefficient D=3.5×10 −9 exp− 72 RT ( kcal/mole) m 2 sec −1 . Experimental errors on the above numerical values are large and give, for the preexponential and energy terms, respectively: 2.10 −7<D 0<3.10 −10 m 2 sec − 62<Q<82 kcal/mole . Nevertheless these results seem in good agreement with those deduced from high-temperature and low-stress creep experiments. The theoretical aspect of self-diffusion of yttrium in Y 2O 3 is studied in terms of point defects and lattice disorder due to the equilibrium between the oxide and its environment. This last part is confined to the restricted range of high oxygen partial pressure in which oxygen interstitials are supposed to be majority defects. Intrinsic and extrinsic diffusion behavior are both considered on the basis of a vacancy diffusion mechanism.