Phonon-Mediated Low-Pressure Superconductivity in Ternary Hydride Ba–CH₄

To explore the low-pressure and high-temperature superconductivity of light-element compounds, based on the first-principles calculations, we have investigated the crystal structure, stability, metallization, and possible superconductivity of a ternary hydride Bax(CH4)1–x in the pressure range of 0–100 GPa. At low pressures, the Ba-intercalating CH4 solid retains the characteristics of molecular crystals. The results show that two phases of Bax(CH4)1–x can realize metallization and superconductivity starting from the low pressure of 10 GPa. The metallization mainly results from the charge transfer from Ba to CH4 molecules. The superconducting critical temperature is predicted to exceed 24 K at 20 GPa and reach 43.7 K at 90 GPa. Our results indicate that metal-doped methane is a potential candidate for searching the high-temperature superconductors at low pressures.