Superhard high-entropy dodecaboride with high electrical conductivity

Methods used to enhance the hardness of a material often render a noticeable deterioration of electrical conductivity so that a tradeoff must be made between conductivity and hardness. Here, we report a counterintuitive strategy for the design of superhard materials with superior electrical conductivity. We subsequently synthesized a high-entropy rare-earth dodecaboride that is a highly disordered homogeneous crystalline single phase with the UB-type structure. This material exhibits a sufficient enhancement of hardness (∼43.1 GPa under a load of 0.49 N) over its constituent binary dodecaborides, while possessing a high electrical conductivity (∼1.96 ×10 S/m) comparable to that of pure metals. A high content of lightweight boron enables a substantial reduction in its density compared with other hard metal compounds. The extraordinary metal-like conductivity, together with high hardness and low density, makes it find promising applications as body armors and hard conductors under extreme conditions.