Phase Transitions of BiVO4 under High Pressure and High Temperature

We have studied the occurrence of phase transitions in two polymorphs of BiVO4 under high-pressure and high-temperature conditions by means of X-ray diffraction measurements. The fergusonite polymorph undergoes a phase transition at 1.5(1) GPa and room temperature into a tetragonal scheelite-type structure. The same transition takes place at 523(1) K and ambient pressure. A second phase transition takes place at room temperature under compression at 16(1) GPa. The transition is from the tetragonal scheelite structure to a monoclinic structure (space group P2(1)/c). All observed phase transitions are reversible. The zircon polymorph counterpart also transforms under compression into the scheelite-type structure. In this case, the transitions take place at 4.3(1) GPa and room temperature and at 653(1) K and ambient pressure. The zircon-scheelite transition is nonreversible. The experiments support that the fergusonite-scheelite transformation is a second-order transition and that the zircon-scheelite transformation is a first-order transition. Finally, we have also determined the compressibility and the thermal expansion of the fergusonite, scheelite, and zircon phases.