Electronic Structure and High-Temperature Thermochemistry of Oxygen-Deficient BaMO₃ (M = Ti – Cu) Perovskites

Alkaline-earth perovskites are of particular interest for high-temperature energy conversion processes because of their mixed-valence charge states, which significantly affect their chemical and thermal stability. However, in many cases, the thermochemical properties and stabilities of such perovskites under high-temperature conditions remain uncharacterized. We present here a systematic study of the stability, electronic structures, and thermochemical properties of oxygen-deficient BaMO3 (M = Ti – Cu) perovskites using accurate first-principles calculations. The electronic structure across this series of perovskites varies from a semiconductor/insulator to a ferromagnetic and ultimately metallic character, and this leads to a change in the intrinsic stability of the perovskite lattices of more than 700 kJ mol–1. However, these intrinsic trends are disrupted significantly when explicit thermochemical corrections, relevant to high-temperature applications, are included in reduction free energies. The key factor in this respect is the temperature-dependent entropic contribution, which is distinct for each perovskite. We demonstrate that this is a reflection of the unique instabilities of each perovskite structure at high temperatures.