Dissociation products and structures of solid H2S at strong compression

TL;DR

This study combines theoretical and experimental methods to identify and characterize new decomposition products of compressed H2S, revealing their structures and superconducting properties under high pressure.

Contribution

It reports the discovery of new stable stoichiometries like H4S3 and provides insights into their structures and superconducting behavior at high pressures.

Findings

H4S3 is stable between 25-113 GPa.

H3S and H4S3 are confirmed experimentally at high pressure.

H2S mainly causes superconductivity below 100K.

Abstract

Hydrogen sulfides have recently received a great deal of interest due to the record high superconducting temperatures of up to 203 K observed on strong compression of dihydrogen sulfide (H2S). A joint theoretical and experimental study is presented in which decomposition products and structures of compressed H2S are characterized, and their superconducting properties are calculated. In addition to the experimentally known H2S and H3S phases, our first-principles structure searches have identified several energetically competitive stoichiometries that have not been reported previously; H2S3, H3S2, and H4S3. In particular, H4S3 is predicted to be thermodynamically stable within a large pressure range of 25-113 GPa. High-pressure room-temperature X-ray diffraction measurements confirm the presence of H3S and H4S3 through decomposition of H2S that emerge at 27 GPa and coexist with residual H2S, at least up to the highest pressure studied in our experiments of 140 GPa. Electron-phonon coupling calculations show that H4S3 has a small Tc of below 2 K, and that H2S is mainly responsible for the observed superconductivity of samples prepared at low temperature (<100K).