Free energy of defect formation: Thermodynamics of anion Frenkel pairs in indium oxide

The temperature-dependent free energies, entropies, and enthalpies for the formation of anion Frenkel pairs in In₂O₃ are reported, as calculated within the Mott-Littleton embedded-cluster approach, by exploiting the relationship between isobaric and isochoric thermodynamic processes. Our model for In₂O₃ proves particularly successful in the reproduction and prediction of the thermoelastic properties, including heat capacity, compressibility, and thermal expansion in the high-temperature regime. We employ this model to predict the thermal behavior of oxygen vacancy and oxygen interstitial defects. Aggregation of the point defects is energetically favorable and dampens the temperature dependence of defect formation, with a decreased free volume of defect formation. The results highlight the contribution of point defects to the high-temperature thermal expansion of indium sesquioxide, as well as the appreciable temperature dependence of the thermodynamic potentials, including enthalpy and free energy, associated with defect formation in general. A transferable procedure for calculating such thermodynamic parameters is presented.