The discovery of high-temperature superconductivity in hydrogen-rich compounds has fueled the enthusiasm for finding materials with more promising superconducting properties among hydrides. However, the ultrahigh pressure needed to synthesize and maintain high-temperature hydrogen-rich superconductors hinders the experimental investigation of these materials. For practical applications, it is also highly desired to find more hydrogen-rich materials that superconduct at high temperatures but under relatively lower pressures. Based on first-principles density functional theory, we calculate the electronic and phonon band structures for a ternary borohydride formed by intercalating ${\mathrm{BH}}_4$ tetrahedrons into a fcc potassium lattice, ${\mathrm{KB}}_2{\mathrm{H}}_8$. Remarkably, we find that this material is dynamically stable and one of its $s{p}^3$-hybridized $\sigma$-bonding bands is metallized (i.e., partially filled) above a moderate high pressure. This metallized $\sigma$-bonding band couples strongly with phonons, giving rise to a strong superconducting pairing potential. By solving the anisotropic Eliashberg equations, we predict that the superconducting transition temperature of this compound is 134–146 K around 12 GPa.

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• Electron-phonon coupling
• Pressure effects
• Superconducting phase transition
• High-temperature superconductors
• Hydrides
• Eliashberg theory
• First-principles calculations
• Methods in superconductivity