Superconductivity and high hardness in scandium-borides under pressure.

Exploration of new superconducting or superhard transition-metal borides has attracted extensive interest in the past few decades. In this study, we conducted comprehensive theoretical investigations in the scandium-boron binary system by employing a structural search method based upon first-principles density functional theory. Among the six predicted superconducting scandium-borides, ScB (3̄) has the highest superconducting transition temperature = 12.3 K and a Vickers hardness of 12.6 GPa at ambient pressure. The superconductor ScB (2/) has = 3.6 K and a high Vickers hardness of 25.5 GPa at ambient pressure. Further analysis indicates that the previously synthesized ScB (4) is of superhardness. Our discoveries not only enrich the phase diagram of scandium-borides, but also pave the way for future experimental validations and potential applications of superconducting scandium-borides in industry.