Pressure-induced decomposition of β-SnWO4

Abstract

This study reports the decomposition of β-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 β-SnWO4 to α-SnWO4. Our investigation into the causes of the observed decomposition revealed that it is unrelated to any mechanical or dynamic instabilities, being most likely related to the frustration of the β−α transition, since such a transition would involve 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 β-SnWO4. Furthermore, the elastic constants and moduli, as well as the pressure dependence of Raman and infrared modes of β-SnWO4, were derived from density-functional theory calculations. Several phonon modes exhibited softening, and three cases of phonon anti-crossing were observed.