High-temperature superconductivity in M 2 BH 6 hydrides under near ambient pressure

Hydrogen-rich compounds that exhibit high-temperature superconductivity typically require extreme pressures, which severely limits their practical applicability. Recent theoretical predictions of the complex hydride Mg2IrH6 have introduced a new family of M2XH6-type hydrides, highlighting the potential for high-temperature superconductivity at near-ambient pressure. Motivated by this, we have performed high-throughput first-principles investigations of the M2XH6 family (M = IA, IIA, IIIA, IIB metals; X = B, C, N) to identify dynamically stable hydrides and explore their superconducting properties. Eleven boron-based hydrides, M2BH6 (M = Li, Na, K, Rb, Cs, Ca, Sr, Ba, Sc, Y, La), featuring BH6 octahedral units have been identified. Notably, Li2BH6 is dynamically stable down to 16 GPa and exhibits a superconducting critical temperature of 121.25 K. Electronic structure and phonon analyses indicate that high-frequency hydrogen vibrations from strong B–H covalent bonding, reinforced by light Li atoms, dominate the electron–phonon coupling. In contrast, noble-metal-based Li2XH6 compounds (X = Cu, Ag, Au) exhibit distinct superconducting mechanisms, driven by d electrons at the Fermi level and low-frequency metal vibrations. These findings expand the compositional space of the M2XH6 family and highlight Li2BH6 as a promising candidate for near-ambient-pressure high-Tc superconductivity.