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 s 2 electron lone pair and a d 0 electronic configuration, such as BiVO 4, possess favorable band gaps. BiVO 4 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 s 2 and d 0 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 BiVO 4, and temperature-dependent local-scale distortions are revealed using neutron total scattering methods. Together, these suggest the polar properties of BiVO 4 are related to local-scale distortions induced by the Bi 3+ 6 s 2 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.