The synthesis of hydrogen sulfides, with the potential of high-temperature superconductivity, was recently proposed at high $T_c$ = 203 K. It motivated us to employ an ab initio approach for the predictions of crystal structures to find the stable scandium hydrides. In addition to the earlier predicted three stoichiometries of ScH, ${\mathrm{ScH}}_2$, and ${\mathrm{ScH}}_3$, we identify three other metallic stoichiometries of ${\mathrm{ScH}}_4, {\mathrm{ScH}}_6$, and ${\mathrm{ScH}}_8$, which show superconductivity at significantly higher temperatures. The phases of ${\mathrm{ScH}}_4$ and ${\mathrm{ScH}}_6$, whose stability does not require extremely high pressures ($<150$ GPa with ZPE), are primarily ionic compounds containing exotic quasimolecular ${\mathrm{H}}_2$ arrangements. The present electron-phonon calculations revealed the superconductive potential of ${\mathrm{ScH}}_4$ and ${\mathrm{ScH}}_6$ with estimated $T_c$ of 98 K and 129 K at 200 GPa and 130 GPa, respectively. The superconductivity of ${\mathrm{ScH}}_n$ stems from the large electron-phonon coupling associated with the wagging, bending, and intermediate-frequency modes attributed mainly to the hydrogen atoms.

• Received 24 May 2017
• Revised 14 August 2017

DOI:https://doi.org/10.1103/PhysRevB.96.094513