ABSTRACT
Single phase tetragonal Zr1-xCexO2 solid solution was prepared by annealing at 627°C the c’-ZrO2, which was obtained by quenching after sintering at 1660° or 1760°C, where the c’-ZrO2 was defined as cubic or tetragonal phases whose axial ratio c/a (tetragonality) equals 1. The lattice parameter and cell volume increased but the tetragonality decreased with CeO2 content. The c’ → t’ transformation was a thermally activated process with an activation energy of 113 kJ/mol, which was estimated by measuring the time dependence of the t’- fraction by X-ray diffraction. This value indicates that the c’→t’ transformation is controlled by oxygen diffusion. In fact, it did not occur in vacuum. The c’→t’ cation-diffusionless transformation was clearly distinguished from the cation-diffusional phase separation t’ → (t + c) which occurred above 900°C in the TTT diagram. Reversible c’ ↔t’ transformation was observed in 65mol%CeO2-ZrO2. The t’→c’ transformation temperatures were located in the vicinity of the cubic solubility limit within the (c+t) two-phase region. The t’→c’ transformation occurred without oxygen-concentration change in 65mol%CeO2-ZrO2.
