A Brief Review of the Effects of Pressure on Wolframite-Type Oxides

Abstract

Abstract:In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites, the cation-oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and the changes in the band-gap energy have also been analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research avenues of wolframites under compression have also been evaluated.

Electronic properties and high-pressure behavior of wolframite-type CoWO4

“…Akin to what was observed for MnWO 4 , in CoWO 4 the unfilled 3d states of Co contribute to the bottom of the conduction band. These d states are pushed down in energy by pressure, contrary to what happens for wolframites with filled d states such as MgWO 4 , ZnWO 4 , and CdWO 4 18,37. On the other hand, for all of the mentioned compounds, the top of the valence band is unaffected by pressure.…”

Synthesis, Characterization, and Crystal Structure Determination of a New Lithium Zinc Iodate Polymorph LiZn(IO3)3

“…Li + ionic conductivity [48,49] as well as highly anisotropic compression and thermal expansion are thus expected [50]. Other properties such as the bulk modulus could be estimated from empirical relations, assuming that compression is dominated by the ZnO 6 and LiO 6 octahedral units, from the Zn-O and Li-O bond distances and the formal charge of Zn and Li [51]. The obtained value was 55 GPa.…”

A High-Pressure Investigation of the Synthetic Analogue of Chalcomenite, CuSeO3∙2H2O

“…All of these studies have been carried out at ambient pressure. However, it is known that high pressure (HP) could lead to interesting phenomena in minerals, including pressure-driven phase transitions [10]. In particular, HP studies have been performed in hydrated minerals related to chalcomenite, like FeSO 4 •H 2 O and MgSO 4 •H 2 O, leading to results relevant for Earth and Planetary Sciences [11,12].…”