Phase Relation of ZrO2-YO1.5-TiO2 Ceramics Prepared by Sol-Gel Method: Solid Solubility of TiO2 in Fluorite Phase

Phase relationship in ZrO2-YO1.5-TiO2 system, solid solubility of TiO2 in yttria stabilized zirconia (YSZ) and phase stability have been investigated for the samples prepared by sol-gel method after the heat treatment between 1073 and 1923K for 10 to 100h using a powder X-ray diffraction analysis. The lattice parameter of the fluorite (FC) phase at fixed concentration of yttria was found to decrease linearly with increasing TiO2 concentration by the substitution of Ti4+ for Zr4+ ions. Although decrease in solid-solubility limit of TiO2 in (YO1.5)0.250-(Zr0.750-xTix)O2 with increasing annealing period suggests that the phase relationship obtained in this experiment includes metastability of the solid solution, the phase relationship satisfies the phase rule, except for the composition regime relating the formation of Zr3Y4O12, YO1.5 and Y2Ti2O7. The ternary phase relationships have been given for the annealing conditions of 1923K for 6h, 1773K for 10h, 1473K for 60h, 1273K for 10h and 100h and 1073K for 10h in air. The ternary eutectic temperature was estimated to be about 1823K from the phase relationship and the solid solubility of TiO2 in (YO1.5)0.250-(Zr0.750-xTix)O2 between 1273 and 1773K. The present results suggest that the solid solubility of TiO2 in YSZ is much smaller than the reported value.