X-ray Diffraction and Equation of State of the C-S-H Room-Temperature Superconductor
Abstract
X-ray diffraction indicates that the structure of the recently discovered room temperature carbonaceous sulfur hydride (C-S-H) superconductor is derived from previously established van der Waals compounds found in the H2S-H2 and CH4-H2 systems. Crystals of the superconducting phase were produced by a photochemical synthesis technique leading to the superconducting critical temperature Tc of 288 K at 267 GPa. Single-crystal x-ray diffraction patterns measured from 124 to 178 GPa, within the pressure range of the superconducting phase, give an orthorhombic structure derived from the Al2Cu-type determined for (H2S)2H2 and (CH4)2H2 that differs from those predicted and observed for the S-H system to these pressures. The formation and stability of the C-S-H compound can be understood in terms of the close similarity in effective volumes of the H2S and CH4 components over a broad range of pressures. The relative amounts of carbon and sulfur in the structure is not determined, and denser carbon-bearing S-H structures may form at higher pressures. The results are consistent with hole-doping enhancement of Tc by carbon proposed for the room-temperature superconductivity in this system.
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