Extended layer-by-layer Madelung potential analysis of layered oxyhalide photocatalysts and other layered systems

Abstract

A recent study on Bi₄NbO₈Cl and related Bi-based layered oxyhalide photocatalysts using a layer-by-layer Madelung potential (L²MP) analysis with a sphere model revealed that oxide anions in the fluorite-type slab of Bi₄NbO₈Cl are electrostatically destabilized by the 2nd nearest sublayer composed of the apical oxygen of the perovskite slab. Here we provide an extended L²MP analysis of Bi-based layered oxyhalides using a modified (square-prism) model and apply it to other layered compounds. It is found that consideration of up to the 3rd nearest sublayer is necessary to account for the nearly equal valence band maximum between Bi₂GdO₄X and Bi₄NbO₈Cl. Additionally, BiOX and Bi₂GdO₄X show a distinct X-dependence of the Madelung site potential of oxide anions. The L²MP analysis of Bi₂WO₆, Sr₃Sc₂Cu₂S₂O₅ and Sr₂ScCuSO₃ revealed a sizable contribution of distant layers to their electrostatic potentials. This study demonstrates that this method can be applied to a wide range of layered materials and serves as a powerful guide toward finding composition and layer stacking sequences suitable for photocatalysis and other functions.