Concurrent superconductivity and ultrahardness in pressure-induced BC19

Conventional hard and superhard materials, such as diamond and cubic boron nitride, are attractive for both scientific and industrial applications, but their intrinsically poor electrical conductivity limits broader use. This motivates the exploration of novel materials that combine superior hardness with excellent superconductivity. Herein, we performed a comprehensive structure search of the B–C system under pressures ranging from 0 to 100 GPa using machine-learning-potential (attention-coupled neural network, ACNN) based crystal structure prediction (CALYPSO). A stable BC 19 phase was identified at 50 GPa, featuring a diamond-like covalent framework with metallic character. Interestingly, BC 19 shows anisotropic superconductivity with an estimated superconducting critical temperature ( T c ) of 24 K at ambient pressure. Further analysis indicates that the high superconductivity of BC 19 originates from the strong coupling between the σ electrons and stretching vibrations of the covalent B-C framework. Additionally, BC 19 demonstrates superhard characteristics with a Vickers hardness of 76 GPa, exceeding that of cubic boron nitride. These results suggest that pressure-stabilized BC 19 represents a promising theoretical candidate for concurrent superconductivity and ultrahard mechanical performance.