PHASE-STABILITY AND PHYSICAL-PROPERTIES OF CUBIC AND TETRAGONAL ZRO2 IN THE SYSTEM ZRO2-Y2O3-TA2O5

The cubic (c-ZrO2) and tetragonal zirconia (t-ZrO2) phase stability regions in the system ZrO2-Y2O3-Ta2O5 were delineated. The c-ZrO2 solid solutions are formed with the fluorite structure. The t-ZrO2 solid solutions having a c/a axial ratio (tetragonality) smaller than 1.0203 display high fracture toughness (5 to 14 MPa.m1/2), and their instability/transformability to monoclinic zirconia (m-ZrO2) increases with increasing tetragonality. On the other hand, the t-ZrO2 solid solutions stabilized at room temperature with tetragonality greater than 1.0203 have low toughness values (2 to 5 MPa.m1/2), and their transformability is not related to the tetragonality.