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

Entropic stabilized ABO(3) perovskite oxides promise many applications, including the two-step solar thermochemical hydrogen (STCH) production. Using binary and quaternary A-site mixed {A}FeO(3 )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 nonstoichiometry (delta) accurately. For STCH applications, the E-V(f) distribution, including both the average and the spread, can be optimized jointly to improve delta delta (difference of 6 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.

Automated summary

Using binary and quaternary A-site mixed {A}FeO(3) as a model system, we found that as more cation types are mixed on the A-site, the cell lattice becomes more cubic-like but the local Fe-O octahedrons are more distorted. By comparing different statistical models with experiments, we showed that considering the oxygen vacancy formation energies (E-V(f)) distribution and the vacancy interactions is crucial for accurately predicting the oxygen nonstoichiometry (delta). The E-V(f) distribution, including both the average and the spread, can be optimized to improve delta delta in some hydrogen production levels for solar thermochemical hydrogen production.