Structure and composition of C-S-H compounds up to 143 GPa

We synthesized two C-S-H compounds from a mixture of carbon and sulfur in hydrogen-C : (H2S)(2)H-2 and from sulfur in mixed methane-hydrogen fluids-(CH4)(x)(H2S)((2-x))H-2 at 4 GPa. X-ray synchrotron single-crystal diffraction and Raman spectroscopy have been applied to these samples up to 58 and 143 GPa, respectively. Both samples show a similar Al-2 Cu-type I4/mcm basic symmetry, while the hydrogen subsystem evolves with pressure via variously ordered molecular and extended modifications. The methane-bearing sample lowers symmetry to an orthorhombic Pnma structure after laser heating to 1400 K at 143 GPa. The results suggest that C-S-H compounds are structurally different from a common Im-3m H3S.

Automated summary

The study synthesized two C-S-H compounds from mixtures of carbon and sulfur in hydrogen or sulfur in mixed methane-hydrogen fluids under high pressure conditions. X-ray synchrotron single-crystal diffraction and Raman spectroscopy were used to analyze the structural changes of these compounds under different pressures. The results showed that the structure and symmetry of the compounds evolved with varying pressure, suggesting differences from the common Im-3m H3S structure.