ZIRCONIA CERIA SOLID-SOLUTION SYNTHESIS AND THE TEMPERATURE TIME TRANSFORMATION DIAGRAM FOR THE 1 1 COMPOSITION/

Zirconia-ceria solid solutions of tetragonal symmetry (t' - ZrO2) cont aining 30 to 65 mol% ceria were prepared by annealing c'-ZrO2 at 627-d egrees-C samples sintered at 1660-1760-degrees-C, where c'-ZrO2 is def ined as a cubic or tetragonal phase whose axial ratio c/a (tetragonali ty) is equal to 1. The lattice parameters and the cube root of the uni t cell volumes or the annealed samples increased linearly with the cer ia content but, on the other hand, the axial ratio c/a (tetragonality) decreased to 1.000 at 70 mol%. During the annealing of each sample, t he cell volume decreased because the residual Ce3+ ions were oxidized to the smaller Ce4+. The temperature-time-transformation (TTT) diagram of the 1:1 solid solution was investigated for the c'-t' diffusionles s phase transition and the c'-(t + c) diffusional reaction. The c'-t' transformation was found to behave as a thermally activated process wi th an activation energy estimated to be 113 kJ/mol. This value may ind icate that c'-t' transformation is controlled by oxygen diffusion acco mpanied by dimensional changes of the cerium ions.