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 of hydrogen-related superconductors, we systematically studied the crystal structure and superconductivity of , a hypothetical compound derived from with half its S atoms replaced by group neighbor Se. First-principles structure searches identify three dynamically stable structures for at 200 GPa. Interestingly, all three structures keep the main feature of the cubic structure of , but with different Se substitution positions. Electron-phonon coupling calculations reveal the superconductive potential of the three phases of , with 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 . For comparison, O-substituted was predicted to assume a semiconducting phase with entirely different structural features from . We attribute this difference to the much stronger electronegativity of O (3.44) compared with S (2.58) or Se (2.55).
1 More- Received 8 June 2018
- Revised 29 September 2018
DOI:https://doi.org/10.1103/PhysRevB.98.174101
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