Ta2O5–Y2O3–ZrO2 system: Experimental study and preliminary thermodynamic description

Some aspects of stable and equilibrium phases in the Ta2O5–Y2O3–ZrO2 system have been studied in this work. Phase stability of Ta0.16Y0.16Zr0.68O2 and Ta0.10Y0.10Zr0.80O2 has been studied by X-ray powder diffraction. A secondary phase segregation of YTaO4 has been observed in both compositions below 1500 °C. However, once treated at 1500 °C, YTaO4 phase disappears. The preliminary phase diagram of the Ta2O5–Y2O3–ZrO2 system at 1200 °C and 1500 °C have been constructed using THERMOCALC package. Thermodynamic description is obtained by critically evaluating experimental data on the binary systems Y2O3–Ta2O5 and Ta2O5–ZrO2. Binary system data have been combined and parameters for ternary tetragonal and cubic structures have been assessed to construct ternary phase diagram. Calculated isothermal section at 1200 °C is similar to 1500 °C. There is no change in the tetragonal solid solution region observed with temperature, which indicates the same equilibrium phases at 1500 °C and at 1200 °C.