Phonon-mediated high-temperature superconductivity in the ternary borohydride KB2H8 under pressure near 12 GPa

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 BH₄ tetrahedrons into a fcc potassium lattice, KB₂H₈ . Remarkably, we find that this material is dynamically stable and one of its s p³ -hybridized σ -bonding bands is metallized (i.e., partially filled) above a moderate high pressure. This metallized σ -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.