Understanding the response of BiVO4 to pressure

Bismuth vanadate (BiVO4) has been identified as a promising photocatalyst to produce hydrogen by water splitting and for the conversion of CO2 to hydrocarbons. Both BiVO4 and LaNbO4 undergo a temperature dependent transition from the monoclinic fergusonite structure (I2/a) to the tetragonal scheelite (I41/a) structure at approximately the same temperature, but whereas the monoclinic distortion in LaNbO4 is reported to increase with pressure, BaVO4 is a rare example of an oxide that shows an increase in symmetry upon application of pressure. Variable pressure neutron diffraction data will be measured for BiVO4 and LaNbO4 to test the postulate that the transition from long range ordering of the Bi 6s2 lone pair electrons in the monoclinic structure to disordered in the tetragonal structure of BiVO4 reduces the compressibility of the BiO8 polyhedra resulting in the unusual properties of this material. Neutron PDF measurements have revealed local distortions of the BiO8 polyhedra that are incompatible with the long-range tetragonal symmetry, the role of such local distortions on the compressibility will be established.