Self-Diffusion of Er and Hf in Polycrystalline Er2O3-Stabilized HfO2

Tracer self-diffusion coefficients for Er and Hf were measured in polycrystalline Er₂O₃-stabilized HfO₂ (fluorite phase) at compositions between 10 and 40 mol% Er₂O₃ and temperatures between 1700° and 2033°C. In some instances, grain-boundary coefficients were also determined. The Hf volume coefficients were generally slightly smaller than Er coefficients, but neither showed a strong composition dependence, a finding most likely attributable to extensive clustering of charged defects which apparently rendered a large proportion of the "notional" defects essentially immobile. The activation energies for volume coefficients were very large, ranging from 630 to 760 kJ-mol⁻¹, and generally decreased with increasing Er₂O₃ content.