Thermodynamics and superconductivity of SxSe1−xH3

Abstract

The compression of SH2 and its subsequent decomposition to SH3, presumably in a cubic Im3¯m structure, has led to the discovery of conventional superconductivity with the highest measured and confirmed Tc to date, 203 K at 160 GPa. Recent theoretical studies suggest that a mixture of S with other elements of the chalcogen group could improve the superconducting temperature. Here, we present a detailed analysis of the thermodynamic properties of S and Se mixtures in the bcc lattice with Im3¯m symmetry using a cluster expansion technique to explore the phase diagram of SxSe1−xH3. In contrast to earlier reports, we find that S0.5Se0.5H3 is not stable in the pressure range between 150 and 200 GPa. However, phases at compositions S0.2Se0.8H3,S0.3¯Se0.6¯H3, and S0.6Se0.4H3 are stable at 200 GPa, while additional phases at S0.25Se0.75H3 and S0.75Se0.25H3 are accessible at lower pressures. Electron-phonon calculations show that the values of Tc are consistently lower for all ternary phases, indicating that mixtures of S and Se with H might not be a viable route towards compounds with improved superconducting properties.

Source-reported materials — not catalogue approval

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