Phase Relations at 1500°C in the Ternary System ZrO2-Y2O3-TiO2

Phase relations at 1500°C in the ternary system ZrO2- Y2O3-TiO2have been determined by powder X-ray diffraction of samples prepared by standard solid state mixing and also by ball milling. A large region of this ternary oxide system was shown to exhibit the defect cubic fluorite structure and to encompass compositions containing very high oxygen vacancy concentrations up to 16%, e.g., Zr0.21Y0.62Ti0.17O1.69. We have accurately determined the maximum extent of the defect fluorite phase, at low concentrations of yttrium/high concentrations of titanium. From previous studies this region of the solid solution is expected to yield compositions which exhibit the optimum mixed ionic and electronic conducting properties for electrochemical applications. We have determined that at 1500°C up to 18 atom% Ti4+can be dissolved into ZrO2stabilized in the cubic fluorite structure by the presence of 14 to 20 atom% Y. Trends in composition and unit cell parameter are discussed.