Increasing Symmetry under Pressure: Squeezing the 6 s 2 Lone Pairs in BiVO4

Metal oxides containing cations with an s2 electron lone pair possess favorable band gaps for photocatalysis. Understanding the stereochemical role of the lone pair is important for tuning their physical properties. Here, we present a detailed investigation of the pressure-dependent structure of the well-known photocatalyst BiVO4. We probe this behavior using a combination of neutron powder diffraction (NPD), neutron pair distribution function (NPDF), and density functional theory (DFT) calculations. Our analysis reveals that that the Bi3+ lone pair is suppressed in the high-pressure tetragonal phase, forming a symmetric electron distribution. This contrasts with the tetragonal phase at high temperature and ambient pressure, where localized lone pair distortions have been observed. Additional NPD measurements on LaNbO4, which lacks a cation lone pair, demonstrate the structural distortions expected in fergusonite structured metal oxides, while revealing new pressure-dependent behavior below 7.3 GPa that warrants further investigation.