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.