Oxygen-Storage Materials BaYMn₂O_5+δ from the Quantum-Chemical Point of View

The experimentally known perovskite-like materials BaYMn 2 O 5+δ (δ = 0, 0.5, 1) are characterized by a remarkably reversible oxygen-storage capacity at a moderate 500 °C. We try to elucidate the local structures of the vacancy arrangements in these compounds taking place after an oxygen release. This is done for the three compounds with the help of both ab initio total-energy calculations of density-functional quality and using classical structure rationale. Our results are compared with experimental structure findings. We further calculate oxygen-vacancy formation energies and predict the pathways of the oxygen atoms through the crystal by using NEB (nudged elastic band) calculations. Structure diagrams of the most likely energy pathways for oxygen migration are presented. Finally, thermodynamic considerations of the oxygen intake are carried out based on quasiharmonic phonon calculations and compared with experimental data. The theoretical molar reaction enthalpy for oxidizing BaYMn 2 O 5 to BaYMn 2 O 6 matches the experimental value.