Hydrogen sulfide at high pressure: change in stoichiometry

TL;DR

This study explores how hydrogen sulfide changes its structure and composition under high pressure, revealing new compounds and supporting the understanding of record-high superconductivity in H3S.

Contribution

It provides experimental evidence of new hydrogen-sulfide compounds at high pressures and supports theoretical predictions of their structures and stability.

Findings

H2S becomes unstable and forms new compounds at high pressure

H3S exhibits a record-high superconducting transition temperature

Multiple new sulfur-hydrogen compounds are predicted to be stable at high pressure

Abstract

Hydrogen-sulfide (H2S) was studied by x-ray synchrotron diffraction (XRD) and Raman spectroscopy up to 150 GPa at 180-295 K and by quantum-mechanical variable-composition evolutionary simulations. The experiments show that H2S becomes unstable with respect to formation of new compounds with different structure and composition, including Cccm and a body-centered-cubic (bcc) like (R3m or Im-3m) H3S, the latter one predicted previously to show a record-high superconducting transition temperature, Tc of 203 K. These experiments provide experimental ground for understanding of this record high Tc. The experimental results are supported by theoretical structure searches that suggest the stability of new H3S, H4S3, H5S8, H3S5, and HS2 compounds at elevated pressures.