Anab initiostudy of WO₃under pressure up to 30 GPa

Abstract

High-pressure polymorphs of WO3 have been studied with a first-principles pseudopotential method. The medium-range (0.01–20 GPa) and high-range (20–30 GPa) polymorphs have been characterized and are compared with recent experimental results. The main new feature is the appearance of a sevenfold coordinated tungsten in the high-pressure polymorph. The subtle phase transitions that were induced from Raman spectra evolutions have not been confirmed. However, changes in the W–O distances and O–W–O and W–O–W angles may explain the changes in Raman spectra.

High-pressure Raman scattering and x-ray diffraction of phase transitions in MoO3

“…Comparing our results with similar compounds, it is interesting to note that WO 3 has a first-order phase transition to monoclinic P2 1 / c at 24 GPa. 34,35 In addition, the results of Raman spectra further confirm the P2 1 / c space group for MoO 3 -III, which is a distortion of the ReO 3 structure, analogous to ␤-MoO 3 . In the spectrum collected at 28.3 GPa, the Rietveld refinements converge to the structure model of MoO 3 -III with residuals Rwp = 3.0%, as shown in Fig.…”

Tuning the Photoresponse of Nano‐Heterojunction: Pressure‐Induced Inverse Photoconductance in Functionalized WO3 Nanocuboids

“…[37] Earlier experimental studies and ab initio calculations suggested that these changes are related to a decrease of the W-O-W angles due to WO 6 octahedral tilting, leading to volume reduction under pressure. [38] The affected W-O stretching modes involving oxygen atoms also showed expected behavior. At 28 GPa, M1 phase transformed into a monoclinic-II phase (M2) (P2 1 /c) with sevenfold tungsten coordination by oxygen atoms.…”

“…At 28 GPa, M1 phase transformed into a monoclinic-II phase (M2) (P2 1 /c) with sevenfold tungsten coordination by oxygen atoms. [38] Beyond 28 GPa, the M2 phase persisted up to 34 GPa. It is clear that the photoconductance changes occurred at similar pressures of phase transitions, suggesting the close relationship between the photoconductivity and crystal structure.…”

“…This result indicates that the pressure strongly affected the longer WO bonds, in agreement with the previous studies. [38] Above 6.5 GPa, the compression resulted in a new peak at about 1.91 Å and led to the narrowing of the other two maxima at about 1.8 and 2.1 Å. The ratio of the peak areas corresponding to the coordination numbers is 3:2:1 (WO 3 O 2 O 1 ) in the pressure range of 8.4-24 GPa, and 2:3:1 (WO 2 O 3 O 1 ) in the pressure range of 29-34 GPa, encompassing the structural transition in WO 3 .…”

“…Second, those located in a highly symmetric environment (weakly distorted W 5+ O 6 octahedron) with an average WO bond length of about 1.91 Å; such a bond length is typical for reduced tungsten ions and can be found, for example, in cubic Na x WO 3 . [42] Within such a model, the samples in the G3 group (Table 1) [38,43] de Wijs et al demonstrated that the electronic structure strongly correlates with the distortions of the WO 6 octahedra and their mutual orientation. [44] We also observed octahedral distortion in Raman spectroscopy as well as our XAS results, which indicate the structural and electronic transition.…”