Anomalous Photovoltaic Effect in Centrosymmetric Ferroelastic BiVO₄

The anomolous photovoltaic (APV) effect is an intriguing phenomenon and rarely observed in bulk materials that structurally have an inversion symmetry. Here, the discovery of such an APV effect in a centrosymmetric vanadate, BiVO₄, where noticeable above-bandgap photovoltage and a steady-state photocurrent are observed in both ceramics and single crystals even when illuminated under visible light, is reported. Moreover, the photovoltaic voltage can be reversed by the stress modulation, and a sine-function relationship between the photovoltage and stress directional angle is derived. Microstructure and strain-field analysis reveal localized asymmetries that are caused by strain fluctuations in bulk centrosymmetric BiVO₄. On the basis of the experimental results, a flexoelectric coupling via a strain-induced local polarization mechanism is suggested to account for the APV effect observed. This work not only allows new applications for BiVO₄ in optoelectronic devices but also deepens insights into the mechanisms underlying the APV effect.