The Local-Scale Origin of Ferroic Properties in BiVO₄

Earth-abundant metal oxides are excellent candidates for photocatalytic applications due to their low cost and high stability in aqueous solutions. Materials that contain a combination of metal cations with an s² electron lone pair and a d⁰ electronic configuration, such as BiVO₄, possess favorable band gaps. BiVO₄ has also been reported to possess noncentrosymmetric polar properties, such as flexoelectricity, piezo-photocatalysis, and an anomalous photovoltaic effect, despite its centrosymmetric crystal structure. Here, it is shown how centrosymmetric materials possessing s² and d⁰ cations can display "hidden" local-scale features, often ignored by conventional crystallography, that influence their physical properties. Anomalous peak shapes are observed in the high-resolution synchrotron X-ray powder diffraction of BiVO₄, and temperature-dependent local-scale distortions are revealed using neutron total scattering methods. Together, these suggest the polar properties of BiVO₄ are related to local-scale distortions induced by the Bi³⁺ 6s² electron lone pairs. This demonstrates the possibility of engineering specific interatomic distances between lone pair-bearing cations and the anion sublattice, creating new opportunities for photocatalytic and polar materials from compounds with long-range centrosymmetric structures.