Nonstoichiometry of ZrO2 and Its Relation to Tetragonal-Cubic Inversion in ZrO2

The system Zr-O was studied in the composition range 50 to 66.7 at.% O by metallographic analysis, high-temperature X-ray analysis, and lattice parameter determinations at room temperature. The solubility of zirconium in zirconia was determined from 1200° to 2000°C, and the cubic-tetragonal inversion temperature of ZrO₂ was shown to be lowered to approximately 1490°C for samples containing α-Zr and oxide phase. Alpha zirconium has greater solubility in the cubic phase than in the tetragonal phase, and the inversion is revealed, in samples quenched from the cubic field, by the exsolution of α-Zr, which is metallographically characterized as striations. At room temperature, the striations are oriented with the 111 and 11° planes of monoclinic zirconia.