Pressure-induced phase transitions and decompositions of Sr–S compounds

Abstract

The processes involved in the high-pressure phases of Sr–S compounds and the pressure-induced decomposition into strontium and sulfur are investigated using a structure prediction approach combined with first-principles calculations. The compression of Sr–S compound leads to its decomposition into strontium and sulfur at 794 GPa, which contradicts the general intuition that pressure stabilizes and densifies materials. With increasing pressure, the combined effect of the ΔPV and ΔU term increases the enthalpy difference, ultimately leading to the decomposition of the Sr–S compound. Moreover, the analysis based on molecular orbital theory reveals that pressure induces an increased population of antibonding states, consequently reducing the stability of the compound and promoting its decomposition. Furthermore, the analysis of atomic interactions reveals that under pressure, the reduction of charge transfer between atoms causes a decrease in electrostatic interactions, thereby weakening the stability of the compound and resulting in its decomposition into strontium and sulfur atoms. This work not only demonstrates the high-pressure properties of Sr–S compounds but also provides insight into understanding other high-pressure alkaline-earth sulfides.