Volume and Grain Boundary Diffusion of Hf in Polycrystalline Er ₂ O ₃

Hafnium diffusion was measured in polycrystalline Er 2 O 3 with two impurity levels. A tracer sectioning technique was used and the diffusion coefficients were measured at 1601° to 1970°C. Volume diffusion of Hf showed both extrinsic and intrinsic behavior, with the transition temperature increasing with the impurity level present in Er 2 O 3 . The grain boundary diffusion was apparently extrinsic over the entire temperature interval.