Lattice dynamics study in PbWO4 under high pressure

TL;DR

This study investigates the pressure-induced structural phase transitions in PbWO4 using Raman spectroscopy up to 17 GPa, complemented by ab initio calculations to analyze phonon modes and phase coexistence.

Contribution

It provides detailed experimental data on phase transitions in PbWO4 under high pressure and combines it with theoretical calculations for mode assignment and analysis.

Findings

Identified phase transitions at 6.2 GPa and 7.9 GPa.

Observed phase coexistence from 7.9 to 14.6 GPa.

Assigned Raman modes to different phases using ab initio calculations.

Abstract

Room-temperature Raman scattering has been measured in lead tungstate up to 17 GPa. We report the pressure dependence of all the Raman modes of the tetragonal scheelite phase (PbWO4-I, space group I41/a), which is stable at ambient conditions. Upon compression the Raman spectrum undergoes significant changes around 6.2 GPa due to the onset of a partial structural phase transition to the monoclinic PbWO4-III phase (space group P21/n). Further changes in the spectrum occur at 7.9 GPa, related to a scheelite-to-fergusonite transition. This transition is observed due to the sluggishness and kinetic hindrance of the I-to-III transition. Consequently, we found the coexistence of the scheelite, PbWO4-III, and fergusonite phases from 7.9 to 9 GPa, and of the last two phases up to 14.6 GPa. Further to the experiments, we have performed ab initio lattice dynamics calculations which have greatly helped us in assigning the Raman modes of the three phases and discussing their pressure dependence.