Pressure-induced amorphization and existence of molecular and polymeric amorphous forms in dense SO2

We report here the pressure-induced amorphization and reversible structural transformation between two amorphous forms of SO2: molecular-amorphous and polymeric-amorphous, with the transition found at 26 GPa over a broad temperature regime, 77 - 300 K. The transformation was observed by both Raman spectroscopy and xray diffraction in a diamond anvil cell. The results were corroborated by ab initio molecular dynamics simulations, where both forward and reverse transitions were detected, opening a window to detailed analysis of the respective local structures. The high-pressure polymeric-amorphous form was found to consist mainly of disordered
polymeric chains made of 3-coordinated sulfur atoms connected via oxygen atoms, with few residual intact molecules. This study provides an example of polyamorphism in a system consisting
of simple molecules with multiple bonds.