ScVO₄under non-hydrostatic compression: a new metastable polymorph

Abstract

The high-pressure (HP) behaviour of scandium vanadate (ScVO) is investigated under non-hydrostatic compression. The compound is studied by means of synchrotron-based powder x-ray diffraction (XRD) and optical-absorption techniques. The occurrence of a non-reversible phase transition is detected. The transition is from the zircon structure to the fergusonite-type structure and takes place around 6 GPa with nearly 10% volume discontinuity. XRD measurements on the pressure cycled sample confirm for the first time that the fergusonite-type ScVO can be recovered as the metastable phase at ambient conditions. Raman spectroscopic measurements verify the metastable phase to be of a fergusonite-type phase. Theoretical calculations also corroborate the experimental findings. The fergusonite phase is found to be stiffer than the ambient-pressure zircon phase, as indicated by the observed experimental and theoretical bulk moduli. The optical properties and lattice-dynamics calculation of the fergusonite ScVO are discussed. At ambient pressure the band gap of the zircon (fergusonite)-type ScVO is 2.75 eV (2.3 eV). This fact suggests that the novel metastable polymorph of ScVO can have applications in green technologies; for instance, it can be used as photocatalytic material for hydrogen production by water splitting.

Recent progress on the characterization of the high-pressure behaviour of AVO4 orthovanadates

“…This can be a consequence of the fact that the grains with higher deviatoric strains transform to the scheelite phase at lower pressure. This conclusion is in agreement with observation made in non-hydrostatic experiments [28,37]. In case of scheelite structure, t/G is found to increase from 0.036 at 5 GPa to 0.096 at 25.6 GPa.…”

“…vanadates. Calculations have not only helped to grasp the influence of pressure on the electronic band gap of different polymorphs, but have also contributed to reach a systematic understanding of AVO4 vanadates [34,37,43,44,145,147,148,149]. The contribute to the reduction of Egap [22].…”

“…The explanation to the anisotropic compression of scheelite and zircon is related to the way in which the different polyhedral are connected in each structure and with the circumstance that the GPa -1 and κc = 1.3 × 10 -3 GPa -1 for zircon-type EuVO4 [59] and κa = 1.3 × 10 -3 GPa -1 and κc = 1.9 × 10 -3 GPa -1 for scheelite-type EuVO4 [59]. This anisotropic behaviour is enhanced in the post-scheelite fergusonite-type phase [37,59].…”

Copper Delafossites under High Pressure—A Brief Review of XRD and Raman Spectroscopic Studies

“…Till now the high pressure studies are focused on copper based delafossites with rhombohedral symmetry, however delafossites with hexagonal symmetry have not yet been investigated, and hence systematic investigations on these compounds is required. Another area of research under high pressure is the effect of non-hydrostatic stresses [78] on the crystal structure and band gap of these materials which may result in synthesis of new metastable polymorph with improved properties. Doped delafossites with reduced band gap and increased conductivity can also be investigated under high pressure to obtain compounds with tailor made properties for specific applications.…”

High‐pressure phase transitions and properties of MTO4 compounds with the monazite‐type structure

“…These polymorphs are expected to have a smaller band gap than the monazite‐type polymorphs, that is, close to 2 eV . Thus, they can have applications in green technologies as photocatalytic materials for hydrogen production by water splitting .…”