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 K to 300 K. The transformation was observed by both Raman spectroscopy and X-ray diffraction in a diamond anvil cell. The results were corroborated by ab initio MD simulations, where both forward and reverse transitions were detected, allowing a 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. Our study provides an example of polyamorphism in a system consisting of simple molecules with multiple bonds [1].

[1] Huichao Zhang et al., PNAS 2020, 117, 8736–8742.