Significant enhancement of hardness and stability in the Sc Ta1-B2 transition-metal diborides system

Transition-metal borides have emerged as promising candidates for potential superhard materials due to their remarkable mechanical properties, favorable synthesis conditions and diverse physical properties. However, achieving the requisite hardness for classification as superhard materials in transition-metal borides remains a significant challenge. In this study, we employed a multicomponent strategy to optimize electron band filling, investigating the thermodynamic stability and mechanical properties of Sc x Ta 1− x B 2 (0 ≤ x ≤ 1) transition-metal diborides. Calculations predicted Sc 0.5 Ta 0.5 B 2 as the most promising composition, with its Fermi level located near the pseudogap, resulting in the lowest thermodynamic energy and superior mechanical properties. Experimentally, Sc 0.5 Ta 0.5 B 2 was successfully synthesized under ambient pressure, achieving a hardness of 31.5 GPa under a 4.9 N load, the highest hardness reported for single-phase transition-metal borides. Additionally, Sc 0.5 Ta 0.5 B 2 shows an electrical resistivity of 104.9 μΩ·cm at room temperature, indicating its excellent electrical conductivity. These findings provide critical insights for the design of novel superhard metal materials, achieved through electron filling modifications induced by multicomponent strategies. This approach expands the potential for developing cost-effective, superhard materials, with implications for advancing transition-metal diborides.