CATION INTERDIFFUSION AND PHASE-STABILITY IN POLYCRYSTALLINE TETRAGONAL CERIA-ZIRCONIA-HAFNIA SOLID-SOLUTION

Zr-Hf interdiffusions were carried out at 1350-degrees to 1520-degrees-C for polycrystalline tetragonal solid solutions of 14CeO2.86(Zr1-xHfx)O2 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 x 10(3) exp[-623 (kJ/mol)/RT] cm2/s and grain-boundary interdiffusion parameters by delta-D' = 0.29 exp[-506 (kJ/mol)/RT] cm3/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 CeO2-doped ZrO2 were 11 and 6-mu-m for the solutions with 2 and 10 mol% HfO2 substitution, respectively, both of which are much greater than in the Y2O3-doped ZrO2 solid solution.