Accurate prediction of oxygen vacancy concentration with disordered A-site cations in high-entropy perovskite oxides.

Entropic stabilized ABO₃ perovskite oxides promise many applications, including the two-step solar thermochemical hydrogen (STCH) production. Using binary and quaternary A-site mixed {A}FeO₃ as a model system, we reveal that as more cation types, especially above four, are mixed on the A-site, the cell lattice becomes more cubic-like but the local Fe–O octahedrons are more distorted. By comparing four different Density Functional Theory-informed statistical models with experiments, we show that the oxygen vacancy formation energies ( E V f ) distribution and the vacancy interactions must be considered to predict the oxygen non-stoichiometry (δ) accurately. For STCH applications, the E V f distribution, including both the average and the spread, can be optimized jointly to improve Δδ (difference of δ between the two-step conditions) in some hydrogen production levels. This model can be used to predict the range of water splitting that can be thermodynamically improved by mixing cations in {A}FeO₃ perovskites. [ABSTRACT FROM AUTHOR]