To explore the high-temperature superconductivity of hydrogen-rich compounds at low pressures, we have investigated the crystal structures, electronic and dynamical properties, electron-phonon interactions, and possible superconductivity of the ternary hydride $M{\mathrm{C}}_2{\mathrm{H}}_8$ ($M=$ Na, K, Mg, Al, and Ga) in the low-pressure range of $0–100\mathrm{GPa}$ based on the first-principles calculations. The results show that there is no imaginary frequency in phonon spectra for $M{\mathrm{C}}_2{\mathrm{H}}_8$ at selected pressures which indicates that $M{\mathrm{C}}_2{\mathrm{H}}_8$ is dynamically stable. Furthermore, according to the Eliashberg spectral function under pressures, $M{\mathrm{C}}_2{\mathrm{H}}_8$ is predicted to be superconducting at low pressure. Especially, the superconducting critical temperature ($T_c$) of ${\mathrm{MgC}}_2{\mathrm{H}}_8$ is higher than 55 K at 40 GPa and the $T_c$ in ${\mathrm{AlC}}_2{\mathrm{H}}_8$ reaches 67 K at 80 GPa. Electronic and phonon states and the electron-phonon interactions show that H has a considerable contribution to this ternary hydride superconductor and suggest that increasing the contribution of H to total electron-phonon coupling is a way to design materials with high $T_c$. Our study shows that it is one of the feasible routes to explore the low-pressure and high-temperature superconductivity in ternary carbon-based hydrides.

• Received 8 November 2021
• Revised 8 March 2022
• Accepted 18 March 2022

DOI:https://doi.org/10.1103/PhysRevB.105.104511