Cation Interdiffusion and Phase Stability in Polycrystalline Tetragonal Ceria–Zirconia–Hafnia Solid Solution

Zr–Hf interdiffusions were carried out at 1350° to 1520°C for polycrystalline tetragonal solid solutions of 14CeO 2 ·86(Zr 1‐ x Hf x )O 2 with X = 0.02 and 0.10. Lattice and grain‐boundary interdiffusion parameters were calculated from the concentration distributions by using Oishi and Ichimura's equation. Lattice interdiffusion coefficients were described by D = 3.0 × 10 3 exp[‐623 (kJ/mol)/ RT ] cm 2 /s and grain‐boundary interdiffusion parameters by δ D ' = 0.29 exp[‐506 (kJ/mol)/ RT ] cm 3 /s. The cation diffusivity was lower than the anion diffusivity. The results were compared with diffusivities in the fluorite‐cubic solid solution. The critical grain radii for stabilization of the tetragonal phase in CeO 2 ‐doped ZrO 2 were 11 and 6 μm for the solutions with 2 and 10 mol% HfO 2 substitution, respectively, both of which are much greater than in the Y 2 O 3 ‐doped ZrO 2 solid solution.