Phase behavior and compression of ZrO 2-5.04 wt. % CaO at high pressures

Abstract

Both the baddeleyite and fluorite phases were identified in a commercially produced Ca-doped partially-stabilized zirconia having a composition of ZrO 2-5.04 wt. % CaO. These two phases were observed after sintering at 1300°C for 24 h, but only the fluorite phase was observed after sintering at 1600°C for 4 h. At room temperature and under hydrostatic environment, the baddeleyite phase transforms to the fluorite phase in the pressure range 60 to 90 kbar for the as-received material and in the range 40 to 50 kbar for the sample sintered at 1300°C, and the transitions are reversible. The different transition pressures are likely to be attributed to the different calcium contents in the baddeleyite phase resulting from the sintering process. The high-pressure phase behavior of baddeleyite containing some impurities is in a remarkable contrast to that observed in pure ZrO 2, in which baddeleyite transforms reversibly to an orthorhombic phase near 35 kbar at room temperature. The isothermal zero-pressure bulk modulus for the calciastabilized fluorite phases is calculated to be 1.90 ± 0.15 Mbar from compression data. In comparison with literature data, it seems to suggest that bulk modulus for the fluorite-type zirconia is rather insensitive to the type and the amount of impurities which stabilize it.