Self-Diffusion of Er and Hf in Pure and HfO sub 2 -Doped Polycrystalline Er sub 2 O sub 3

摘要

Using a tracer technique, self-diffusion of Er and Hf was measured over the approximate temperature interval of 1600 to 1970 exp 0 C in pure and HfO sub 2 -doped polycryatalline Er sub 2 O sub 3 . Up to about 10 m/o HfO sub 2 dopant level, the Er self-diffusion coefficients followed a relationship based on cation vacancies. Above 10 m/o HfO sub 2 , deviation from this relationship occurred, apparently due to clustering of cation vacancies and oxygen interstitials around the dopant hafnia ion. The activation energy for the self-diffusion of Er in pure Er sub 2 O sub 3 was 82.2 Kcal/mole and increased with the HfO sub 2 dopant level present. Self-diffusion of Hf was measured in pure Er sub 2 O sub 3 having two impurity levels, and a separation of the grain boundary. The volume diffusion of Hf showed both extrinsic and intrinsic behavior with the transition temperature increasing with the impurity level present in Er sub 2 O sub 3 . The activation energy for Hf volume diffusion in the intrinsic region was high, i.e. 235 -+ 9.5 Kcal/mole. The grain boundary diffusion was apparently extrinsic over the entire temperature interval Very low Hf self diffusion rates were found in both pure and HfO sub 2 doped Er sub 2 O sub 3 compositions. Despite a clustering effect, the HfO sub 2 dopant increased the Hf volume diffusion coefficients. (ERA citation 04:019805)