Stability of FeVO 4 under Pressure: An X-ray Diffraction and First-Principles Study

The high-pressure behavior of the crystalline structure FeVO 4 has been studied by means of X-ray diffraction using a diamond-anvil cell and first-principles calculations. The experiments were carried out up to a pressure of 12.3 GPa, until now the highest pressure reached to study an FeVO 4 compound. High-pressure X-ray diffraction measurements show that the triclinic P 1̅ (FeVO 4 - I ) phase remains stable up to ≈3 GPa; then a first-order phase transition to a new monoclinic polymorph of FeVO 4 (FeVO 4 - II′ ) with space group C 2/ m is observed, having an α-MnMoO 4 -type structure. A second first-order phase transition is observed around 5 GPa toward the monoclinic ( P 2/ c ) wolframite-type FeVO 4 - IV structure, which is stable up to 12.3 GPa in coexistence with FeVO 4 - II′ . The unit cell volume reductions for the first and second phase transitions are Δ V = −8.5% and −13.1%. It was observed that phase transitions are irreversible and both high-pressure phases remain stable once the pressure is released. Calculations were performed at the level of the generalized gradient approximation plus Hubbard correction (GGA+ U ) and with the hybrid Heyd–Scuseria–Ernzerhof (HSE06) exchange-correlation functional in order to have a good representation of the pressure behavior of FeVO 4 . We found that theoretical results follow the pressure evolution of structural parameters of FeVO 4, in good agreement with the experimental results. Also, we analyze FeVO 4 - II (orthorhombic Cmcm, CrVO 4 -type structure) and - III (orthorhombic Pbcn, α-PbO 2 -type structure) phases and compare our results with the literature. Going beyond the experimental results, we study some possible post-wolframite phases reported for other compounds and we found a phase transition for FeVO 4 - IV to raspite (monoclinic P 2 1 / c ) type structure (FeVO 4 - V ) at 36 GPa (Δ V = −8.1%) and a further phase transition to the AgMnO 4 -type (monoclinic P 2 1 / c ) structure (FeVO 4 - VI ) at 66.5 GPa (Δ V = −3.7%), similar to the phase transition sequence reported for InVO 4 .