Theoretical prediction of high-temperature superconductivity above 80 K in boron carbide at ambient pressure

The pursuit of room-temperature superconductors remains a critical challenge in modern science. Here, we perform comprehensive high-throughput structure searches for boron carbide (BC) at ambient pressure using CALYPSO method and first-principles calculations. The structure searches rapidly identify the ground state and two new stable phases,<i>P</i>6₃<i>mc</i>and<i>Pmm</i>2, of BC compounds at ambient pressure. The<i>P</i>6₃<i>mc</i>phase shows remarkable superconductivity with high superconducting transition temperature (<i>T</i>_c) up to 86 K, exceeding the boiling point of liquid nitrogen. Our calculations indicate that the high<i>T</i>_cvalue of the<i>P</i>6₃<i>mc</i>phase of BC arises from its metallized<i>σ</i>-bands and dominant hole-like pockets crossing the Fermi level. Moreover, the<i>Pmm</i>2 phase of BC compound is verified as a superhard superconductor, with<i>T</i>_cof 24 K and Vickers hardness of 44 GPa. These theoretical findings not only enrich the understanding of potential ambient superconductors but also offer promising avenues for the design and synthesis of advanced high-temperature superconductors at ambient pressure.