Self-diffusion of oxygen in single crystal thorium oxide

Abstract

Self-diffusion coefficients of the oxygen ion in a ThO2 single crystal were determined in the temperature range 845–1646°C by the gas–solid isotopic exchange technique using 18O as a tracer. The self-diffusion coefficients determined in the higher temperature range were represented as D=5.73×10−2 exp(−49.9×103/RT) cm2/sec and interpreted to be for intrinsic diffusion due to Frenkel-type defects. Those determined in the lower temperature range were represented as D=1.00×10−6 exp(−17.6×103/RT) cm2/sec and interpreted for extrinsic diffusion. By using these data, it was elucidated that the charge carrier for ionic conduction in ThO2 was the oxygen ion. Activation energies for oxygen permeation in ThO2 and for oxidation of thorium metal were compared with that for oxygen self-diffusion in ThO2.