Pressure-induced amorphization and existence of molecular and polymeric amorphous forms in dense SO ₂

Abstract

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 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 three-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.

Multistep Dissociation of Fluorine Molecules under Extreme Compression

“…Apart from the exceedingly wide range of stable pressures, the structures of these phases show a striking feature, namely the coexistence of atomic, molecular, and polymeric F atoms in the same structure. Although similar abnormal structural features were reported in amorphous N 2 [32] and SO 2 [33] recently, it remains a surprise that all the three different stages of structural evolution of the light p-block elements can coexist in thermodynamically stable crystalline phases. Among four stable structures, Cmca is a pure molecular phase and Fddd is a true atomic phase.…”

High-Pressure Structural Evolution of Disordered Polymeric CS$_2$

“…The electronegativity of C and S is very similar opening more possibilities for polymerization which can occur via C-S bonds as well as via some C=C and S-S bonds. The changes induced by compression are only partially reversible upon decom-pression, in contrast to the recently observed behaviour in SO 2 [23]. Importantly, structural transformations observed upon increasing pressure up to 40 GPa can be explained without assuming chemical disproportionation.…”

Topological Ordering of Memory Glass on Extended Length Scales

“…A widely cited theory for the formation of amorphous materials is Zachariasen’s random network theory, which is adequate for most network glasses under ambient pressure and fast temperature quenching but has seen exceptions for materials under pressure. Applying pressure creates another route to make non-crystalline solids by modulating the enthalpy. − For example, vitreous silica perfectly satisfies Zachariasen’s four-point rules of glass formation. However, quartz and coesite upon pressure-induced amorphization (PIA) feature the edge-shared polyhedra, SiO 5 structural unit, and triple-linked O atoms, ,− all of which are not favored by Zachariasen’s classical theory of a good glass former.…”