Revealing the Unusual Boron-Pinned Layered Substructure in Superconducting Hard Molybdenum Semiboride

Improving the poor electrical conductivity of hard materials is important, as it will benefit their application. High-hardness metallic Mo₂B was synthesized by high-pressure and high-temperature methods. Temperature-dependent resistivity measurements suggested that Mo₂B has excellent metallic conductivity properties and is a weakly coupled superconductor with a T _c of 6.0 K. The Vickers hardness of the metal-rich molybdenum semiboride reaches 16.5 GPa, exceeding the hardness of MoB and MoB₂. The results showed that a proper boron concentration can improve the mechanical properties, not necessarily a high boron concentration. First-principles calculations revealed that the pinning effect of light elements is related to hardness. The high hardness of boron-pinned layered Mo₂B demonstrated that the design of high-hardness conductive materials should be based on the structure formed by light elements rather than high-concentration light elements.