Combining features of complex bonding scheme and multifarious structures, metal borides have received extensive attention as appealing contenders for novel superhard materials with superior electrical conductivity. Based on first-principles calculations, we predicted a metallic superhard boride CaB, consisted by a high-density B−B covalent sublattice arranged in waffle-like B clusters. This special B−B arrangement results in a hitherto maximum hardness value () of 50.1 GPa in binary metal borides. Since the Ca atoms provide electrons to the B cluster, it is beneficial to generating conductive channel in 3D boron network, playing a dominant role in conductivity for CaB. Through the electronic regulation by substituting the alkaline atom at the Ca positions, a superconducting superhard compound CaKB ( = 16.9 K; = 44.1 GPa) can be achieved. We then propose three strategies to design materials with superhard and excellent conductivity/superconductivity properties: (1) the strong average covalent bond strength; (2) the high density of covalent bonds; (3) with appropriate metal atoms to produce carriers. Our work provides innovative way to search for novel ultrahard compounds with favorable electrical conductivity/superconductivity.

中文翻译：

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具有新型华夫饼状硼骨架的金属超硬 CaB12

金属硼化物结合了复杂的键合方案和多种结构的特点，作为具有优异导电性的新型超硬材料的有力竞争者而受到广泛关注。基于第一性原理计算，我们预测了一种金属超硬硼化物 CaB，由排列成华夫饼状 B 团簇的高密度 B−B 共价亚晶格组成。这种特殊的 B−B 排列导致二元金属硼化物的迄今为止最大硬度值 () 为 50.1 GPa。由于Ca原子向B团簇提供电子，有利于在3D硼网络中产生导电通道，对CaB的导电性起主导作用。通过取代Ca位上的碱性原子的电子调控，可以得到超导超硬化合物CaKB（=16.9K；=44.1GPa）。然后，我们提出了三种策略来设计具有超硬和优异导电/超导性能的材料：（1）强的平均共价键强度； (2)共价键密度高； (3)与适当的金属原子结合产生载流子。我们的工作提供了寻找具有良好导电性/超导性的新型超硬化合物的创新方法。