Effect of high-temperature annealing on the valence state of Ce ions and the mechanical properties of (ZrO2)0.972(Y2O3)0.02 (CeO2)0.008 crystals

The effect of high-temperature annealing in various atmospheres on the change in the valence state of Ce ions as well as on the phase composition and mechanical properties of (ZrO2)(0.972)(Y2O3)(0.02) (CeO2)(0.008) crystals has been studied. The crystals have been grown by directional crystallization of the melt in a cold crucible. Electron paramagnetic resonance method has been used to identify Ce3+ ions and their relative amount in crystals. The phase composition and structure of the crystals have been studied by X-ray diffraction and transmission electron microscopy. Hardness and fracture toughness of crystals have been studied by indentation. We show that (ZrO2)(0.972)(Y2O3)(0.02) (CeO2)(0.008) crystals have high values of hardness and fracture toughness. Anisotropy of fracture toughness values has been detected. Thus the observed increase in the fracture toughness of crystals after vacuum annealing is caused by the increasing transformable t phase content and Ce3+ ion concentration. Sequential annealing in oxidizing and reducing atmospheres has led to reversible changes in the valence state of Ce ions as well as in the phase composition and fracture toughness of (ZrO2)(0.972)(Y2O3)(0.02) (CeO2)(0.008) crystals.