High-pressure lattice dynamics in bulk single-crystal BaWO4

TL;DR

This study investigates the pressure-induced phase transitions and lattice dynamics of BaWO4 using Raman spectroscopy up to 16 GPa, supported by ab initio calculations to understand phonon behavior across phases.

Contribution

It provides detailed experimental Raman data on BaWO4 under high pressure and combines it with ab initio calculations for phase transition analysis.

Findings

Identification of phase transition pressures at 6.9 GPa and 9.5 GPa.

Observation of coexistence of phases up to 9.0 GPa.

Assignment of Raman modes to specific phases using calculations.

Abstract

Room-temperature Raman scattering has been measured in barium tungstate (BaWO4) up to 16 GPa. We report the pressure dependence of all the Raman-active first-order phonons of the tetragonal scheelite phase (BaWO4-I, space group I41/a), which is stable at normal conditions. As pressure increases the Raman spectrum undergoes significant changes around 6.9 GPa due to the onset of the structural phase transition to the monoclinic BaWO4-II phase (space group P21/n). This transition is only completed above 9.5 GPa. A further change in the spectrum is observed at 7.5 GPa related to a scheelite-to-fergusonite transition. The scheelite, BaWO4-II, and fergusonite phases coexist up to 9.0 GPa due to the sluggishness of the I?II phase transition. Further to the experimental study, we have performed ab initio lattice dynamics calculations that have greatly helped us in assigning and discussing the pressure behaviour of the observed Raman modes of the three phases.