LATTICE DIFFUSION KINETICS IN Y2O3-STABILIZED CUBIC ZRO2 SINGLE-CRYSTALS - A DISLOCATION LOOP ANNEALING STUDY

The shrinkage rates of small prismatic dislocation loops introduced by high-temperature plastic deformation in 9.4 and 18 mol% Y2O3-stabiliz ed cubic ZrO2 single crystals have been determined via sequential obse rvation of thin transmission electron microscopy foils annealed ex sit u between 1100 and 1300 degrees C. The shrinkage rates of individual l oops were used to determine the diffusivity of the rate-controlling sp ecies, assumed to be Zr point defects (the Zr diffusivity is known to be less than the O diffusivity in this superionic conductor). Both vac ancy and interstitial loops were present and exhibited approximately t he same shrinkage rates. The Zr diffusivities in the 18 mol% Y2O3 allo y were approximately 15 times slower than those in the 9-4 mol% Y2O3 a lloy. However, the activation energies for the two alloy concentration s, 5.3 +/- 0.1 eV, were essentially identical. Traditional point-defec t calculations suggest that cation transport involves a charged-vacanc y cluster ((VOVZr)-V-..'''')'', with an apparent formation enthalpy of 2.8 eV and a migration enthalpy of 2.5 eV. The calculated charged vac ancy cluster concentrations modestly decrease as the doping content in creases. The lower cation diffusivities of the higher solute crystals are attributed to the higher density of yttrium-containing trapping an d blocking centres, (Y'(Zr) V-O(..))(.) and Y'(Zr) respectively.