Assessment of thermodynamic functions in the ZrO2–Nd2O3–Al2O3 system

The thermodynamic database for the ZrO2–Nd2O3–Al2O3 system is derived using the Calphad approach. The compound energy formalism and two-sublattice ionic liquid model are applied for phase descriptions in the system. Thermodynamic parameters for the ZrO2–Nd2O3 and Nd2O3–Al2O3 systems are assessed in this study with special attention to triangulation in the ternary system of ZrO2–Nd2O3–Al2O3. It is demonstrated that the phase equilibria between solid phases in the ternary ZrO2–Nd2O3–Al2O3 system constrain thermodynamic parameters in the binary systems ZrO2–Nd2O3 and Nd2O3–Al2O3. The ternary interaction parameter is assessed for the liquid phase using experimental data on the liquidus surface. Isothermal sections at 1523 and 1923 K, the liquidus surface and several vertical sections are calculated and compared with available experimental data. Several inconsistencies between calculations and experimental data occur because the calculations reveal the existence of a primary crystallisation field for pyrochlore.