Metal borides have been considered as potential high-temperature superconductors since the discovery of record-holding 39 K superconductivity in bulk MgB₂ [1, 2]. In this work, we identified a superconducting yet thermodynamically stable F-43m Sr₂B₅ at 40 GPa with a unique covalent sp³-hybridized boron framework through extensive first-principles structure searches. Remarkably, solving the anisotropic Migdal-Eliashberg equations resulted in a high superconducting critical temperature (T_c) around 100 K, exceeding the boiling point (77 K) of liquid nitrogen. Our in-depth analysis revealed that the high-temperature superconductivity mainly originates from the metalized σ-bonded electronic bands of boron atoms. Moreover, anharmonic phonon simulations suggest that F-43m Sr₂B₅ might be recovered to ambient pressure. Our current findings provide a prototype structure with a full σ-bonded boron framework for the design of high-T_c superconducting borides that may expand to a broader variety of lightweight compounds.

BCS superconductor,First-principles calculation,metal boride