Defects and phase transitions in yttria- and scandia-doped zirconia

Internal friction (IF) experiments were performed on the systems ZrO2 (8–12 mol%)–Y2O3, and ZrO2 (9–12 mol%)–Sc2O3. The following features were found: (i) an IF peak around 500 K in both systems which is assigned to the hopping of trapped oxygen vacancies (ΔH=1.2–1.3 eV); (ii) in polycrystalline materials a high temperature damping background, which is related to cation diffusion; (iii) an order/disorder phase transition at 1450 K in ZrO2–12 mol%Y2O3; and (iv) in ZrO2–Sc2O3 a ferroelastic׃↔ferroelectric phase transition at 750 K from the rhombohedral to the cubic phase. Cation diffusion experiments in ZrO2–Sc2O3 revealed an activation enthalpy for Zr diffusion of 5.3 eV indicating that short- and long-range cation transport is governed by one type of cation diffusion process.