Effect of covalent bonding on the superconducting critical temperature of the H-S-Se system

Abstract

Hydrogen-rich materials have attracted great interest since the recent discovery of superconductivity at 203 K in highly compressed hydrogen sulfide. To probe the role of covalent bonding in determining the Tc of hydrogen-related superconductors, we systematically studied the crystal structure and superconductivity of H6SSe, a hypothetical compound derived from H3S with half its S atoms replaced by group neighbor Se. First-principles structure searches identify three dynamically stable structures for H6SSe at 200 GPa. Interestingly, all three structures keep the main feature of the cubic Im3¯m structure of H3S, but with different Se substitution positions. Electron-phonon coupling calculations reveal the superconductive potential of the three phases of H6SSe, with Tc decreasing (from 195 to 115 K) upon the declining strength of the weakest covalent H-S or H-Se bonds in each structure, thereby highlighting the key role of covalent bonding in determining Tc. For comparison, O-substituted H6SO was predicted to assume a semiconducting phase with entirely different structural features from H6SSe. We attribute this difference to the much stronger electronegativity of O (3.44) compared with S (2.58) or Se (2.55).

Source-reported materials — not catalogue approval

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