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.