Crystal growth and structure of BiVO4

Large crystals of BiVO4 were grown. Extensive twinning can be related to the ferroelastic transition at 528K. The structure of BiVO4 was refined at 4.5, 295 and 566K from powder neutron diffraction data and at 295K from powder X-ray diffraction data by the Rietveld profile technique. Space groups of I41a above and I2b below 528K were confirmed. It is suggested that the transition in BiVO4 is driven by the lone-pair cation Bi3+. The Bi-O polyhedron is regular above the transition but becomes significantly distorted below the transition. This lone-pair distortion increases on cooling from 295 to 4.5K. The V-O tetrahedron remains regular at all temperatures.