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

Abstract

AMO 4 ternary oxides are materials of fundamental and technological importance exhibiting a large variety of functional properties. Members of this family of compounds have multiple potential applications; for instance, as scintillators, thermophosphors, photocatalysts, and cathodoluminescence materials. Studies under high-pressure conditions are valuable for understanding the physical properties and phase behaviour of AMO 4 oxides. In particular, great progress has been achieved in the last decade towards the understanding of the pressure-effects on the structural, vibrational, and electronic properties of AMO 4 materials. Specifically, novel metastable structures with interesting physical properties have been discovered. In this article, a selection of recent results from high-pressure studies on different AMO 4 oxides will be discussed, paying particular attention to orthovanadates. Remarkable phenomena like band-gap and volume collapses as well as phonon softening will be discussed and correlated with structural changes.

High-pressure characterization of multifunctional CrVO4

“…In the last decade, special effort has been put in the study of ternary oxides under pressure and, specifically, to the behavior of orthovanadates [27,28]. CrVO 4 -type compounds are interesting candidates to be studied under pressure since the field map diagram [29] locate them as intermediate structure between quartz-like structures with four-fold coordinated cations and structures with six-fold coordinated cations [30]; for instance, wolframites [31].…”

Crystal structure and phase transition of TlReO4: a combined experimental and theoretical study

“…Their study is not only important for Earth Science [1] and Material Science [2][3][4], but also from a fundamental point of view [5]. A wide variety of these oxides, at ambient conditions, are known to have crystal structures isomorphic to zircon (silicates, phosphates, arsenates, vanadates and chromates) [6], quartz (phosphates and arsenates) [7], scheelite (germanates, molybdates, tungstates, and periodates) [8], wolframite (molybdates, tungstates, and tantalates) [9], M-fergusonite (monoclinic distorted scheelite) [10], pseudoscheelite-type (orthorhombic distorted scheelite) [11], and monasite [12]. Among the MTO 4 oxides, CdWO 4 and PbWO 4 are known as scintillator crystals, ZrGeO 4 and HfGeO 4 are used as phosphors, BaWO 4 , YVO 4 and GdTaO 4 are excellent laser-host materials, and CaMoO 4 and SrWO 4 are known for their use in batteries [13].…”

PrVO4 under High Pressure: Effects on Structural, Optical, and Electrical Properties

“…The structure obtained via this transformation should be rotated using the matrix in order to describe the zircon structure using the same space group and setting that are used for the HP structures. In Figure we can observe that, in spite of the possibility of describing zircon with the same space group as monazite and the similitudes between the edge-sharing V and Pr polyhedral chains in both structures, the monazite structure cannot be obtained via simple displacements of atoms; the transition, in fact, involves not only the displacement and twisting of the polyhedral units of monazite relative to analogous polyhedral units in zircon but also the formation of a new Pr–O bond transforming PrO 8 into PrO 9 . In the case of the second transition, the changes in polyhedral units are more drastic.…”

“…In Figure 11 we can observe that, in spite of the possibility of describing zircon with the same space group as monazite and the similitudes between the edge-sharing V and Pr polyhedral chains in both structures, the monazite structure cannot be obtained via simple displacements of atoms; the transition, in fact, involves not only the displacement and twisting of the polyhedral units of monazite relative to analogous polyhedral units in zircon but also the formation of a new Pr−O bond transforming PrO 8 into PrO 9 . 56 In the case of the second transition, the changes in polyhedral units are more drastic. The displacement and tilting of VO 4 tetrahedra and PrO 9 polyhedra as a consequence of the transition leads to a change in the chemical environment of V and Pr, creating space for the construction of VO 6 distorted octahedra from VO 4 and PrO 10 polyhedra from PrO 9 .…”