Stability of FeVO₄ under Pressure: An X-ray Diffraction and First-Principles Study

Abstract

The high-pressure behavior of the crystalline structure FeVO 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 compound. High-pressure X-ray diffraction measurements show that the triclinic P1̅ (FeVO-I) phase remains stable up to ≈3 GPa; then a first-order phase transition to a new monoclinic polymorph of FeVO (FeVO-II') with space group C2/ m is observed, having an α-MnMoO-type structure. A second first-order phase transition is observed around 5 GPa toward the monoclinic ( P2/ c) wolframite-type FeVO-IV structure, which is stable up to 12.3 GPa in coexistence with FeVO-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. We found that theoretical results follow the pressure evolution of structural parameters of FeVO, in good agreement with the experimental results. Also, we analyze FeVO-II (orthorhombic Cmcm, CrVO-type structure) and -III (orthorhombic Pbcn, α-PbO-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-IV to raspite (monoclinic P2/ c) type structure (FeVO-V) at 36 GPa (Δ V = -8.1%) and a further phase transition to the AgMnO-type (monoclinic P2/ c) structure (FeVO-VI) at 66.5 GPa (Δ V = -3.7%), similar to the phase transition sequence reported for InVO.

Phase transition systematics in BiVO4 by means of high-pressure–high-temperature Raman experiments

“…[53][54][55][56] This functional has been used with success in the study of other vanadates such as InV O 4 and F eV O 4 . 57,58 The Monkhorst-Pack scheme 59 was employed to discretize the Brillouin zone (BZ) integrations with meshes 3×3×3, 4×4×2, and 3×2×4, which correspond to a set of 6, 4, and 6, special k-points in the irreducible BZ for the zircon, scheelite, and fergusonite phases, respectively. In the relaxed equilibrium configuration, the forces are less than 2 meV /Å per atom in each of the Cartesian directions.…”

High pressure crystal structures of orthovanadates and their properties

“…In addition to rare-earth vanadates, another group of materials studied under HP are InVO4 [26], CrVO4 [27], FeVO4 [28], and BiVO4 [29,30]. The main interest in these compounds comes from the fact that they have an optical band gap, which has an optimum value for the non-contaminant production of hydrogen, a zero-emission fuel, from solar energy via the photocatalytic splitting of water [31].…”

Exploring the high-pressure behaviour of polymorphs of AMO4 ternary oxides: crystal structure and physical properties

“…In particular, three different phase transitions have been predicted by calculations and found by XRD measurements for pressures smaller than 12 GPa. 27 One of the HP phases is isomorphic with wolframite (FeVO 4 -IV) and has been found around 6 GPa. FePO 4 is another interesting compound which has been little studied under compression.…”