Low temperature stability of cubic zirconia

A 9 mol% Y2O3-stabilized ZrO2 specimen was annealed in boiling water for 12 00 h, and the phase structure was examined by XRD and the chemical states o f zirconium, yttrium and oxygen were examined by XPS. After annealing, the phase of the specimen remains entirely cubic, and the chemical states of th e elements are not remarkably changed, suggesting that cubic ZrO2 does not degrade to tetragonal or monoclinic phase in the environment known to cause the degradation in tetragonal ZrO2 within 1200 h. The low temperature stab ility of cubic ZrO2 is due to its much higher oxygen vacancy concentration in the space-charge layers and much thinner oxygen vacancy depletion layers in the surfaces and the grain boundaries. The much larger grain size in cu bic ZrO2 also ensures its stability.