First-principles calculations and thermodynamic modeling of the Al ₂O₃-Nd₂O₃ system

Using first-principles calculations, the enthalpies of formation of NdAlO₃ and Nd₄Al₂O₉ from neodymia and alumina are predicted to be -41.1 and -104.5 kJ/mol-form, respectively, and Nd₄Al₂O₉ is predicted to be a stable compound at all temperatures up to its peritectic decomposition temperature. In the case of NdAlO₃, where reported experimental enthalpies of formation differ, our predicted value is used to determine which experimental value is more accurate. The enthalpies of formation calculated by the first-principles method are combined with experimental phase equilibria to evaluate the Gibbs energies of phases in the Al₂O₃-Nd₂O ₃ system. The resulting Gibbs energy functions are compared with previous modelings of the system and are shown to be an improvement as more thermochemical data have been included. The combined first-principles/ thermodynamic modeling approach employed in the current work shows promise in enabling the evaluation of important ceramic systems in which experimental thermochemical data are scarce.