Pressure-Induced Decomposition of beta-SnWO4

TL;DR

This paper investigates the high-pressure decomposition of beta-SnWO4 into Sn, SnO2, and WO3, revealing an irreversible process at around 14 GPa, contrasting with previous theoretical predictions and providing detailed experimental and computational insights.

Contribution

It provides the first high-pressure experimental evidence of beta-SnWO4 decomposition and challenges prior theoretical models by showing the process is driven by transition frustration rather than instability.

Findings

Decomposition occurs at 13.97 GPa and is irreversible.

Pressure influences the unit cell volume and phonon modes.

Several phonon modes soften and exhibit anti-crossing phenomena.

Abstract

This study reports the decomposition of beta-SnWO4 into Sn, SnO2, and WO3 induced by static compression. We performed high-pressure synchrotron powder angle-dispersive X-ray diffraction measurements and found that decomposition occurs at a pressure of 13.97(5) GPa and is irreversible. This result contradicts a previous study that, based on density-functional theory calculations and crystal-chemistry arguments, predicted a pressure-driven transition from beta-SnWO4 to alpha-SnWO4. Our analysis indicates that the observed decomposition is unrelated to mechanical or dynamic instabilities. Instead, it likely stems from frustration of the beta-alpha transition, as this transformation requires a change in Sn coordination from octahedral to tetrahedral. The assessment of how pressure influences the volume of the unit cell provided an accurate determination of the room-temperature pressure-volume equation of state for beta-SnWO4. Furthermore, the elastic constants and moduli, as well as the pressure dependence of Raman and infrared modes of beta-SnWO4, were derived from density-functional theory calculations. Several phonon modes exhibited softening, and three cases of phonon anti-crossing were observed.