Pressure-induced high−Tc superconductivity in the ternary clathrate system Y-Ca-H

The hydrogen-rich ternary compounds under high pressure which rely on the synergistic effect of crystal structure and electronic property changes have a good prospect of realizing room temperature superconductivity. Here, we study the structure and superconductivity of the ternary Y-Ca-H system under high pressure using $ab\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}initio$ calculations. We found four unprecedented ternary hydrides with clathrate hydrogen sublattice: $P\text{\ensuremath{-}}3m1\text{\ensuremath{-}}\mathrm{Y}{\mathrm{Ca}}_{2}{\mathrm{H}}_{18}, Fm\text{\ensuremath{-}}3m\text{\ensuremath{-}}{\mathrm{Y}}_{3}\mathrm{Ca}{\mathrm{H}}_{24}, P4/mmm\text{\ensuremath{-}}\mathrm{YCa}{\mathrm{H}}_{20}$, and $Fm\text{\ensuremath{-}}3m\text{\ensuremath{-}}\mathrm{Y}{\mathrm{Ca}}_{3}{\mathrm{H}}_{24}$ which are potential high-temperature superconductors. Strikingly, the superconducting transition temperature of ${\mathrm{Y}}_{3}\mathrm{Ca}{\mathrm{H}}_{24}$ was calculated to be 242--258 K at 150 GPa. The strong electron-phonon coupling and the high electron density of states of hydrogen at the Fermi level play important roles in high-temperature superconductivity. Further analysis suggests that the phonon softening in the mid-frequency region induced by Fermi surface nesting effectively enhances the electron-phonon coupling. We found that the appropriate stoichiometric ratio is crucial for the discovery of new hydrides in the Y-Ca-H system, which would provide ideas for exploring ternary hydrides.