超硬立方BC2N材料与金刚石的比较

摘要最近有实验称成功合成超硬立方BC2N材料，其硬度仅次于金刚石．文章采用第一性原理计算方法，研究立方BC2N晶体材料的理想强度．计算结果显示，虽然立方BC2N晶体具有很大的弹性系数，但材料中化学成分的各向异性和原子键特性随外加应力变化的非线性性质限制了立方BC2N晶体的强度．最硬的立方BC2N晶体结构的硬度应低于立方BN，后者为目前已知的第二硬材料．实验中观测到的立方BC2N材料的超硬特性应源自材料中的纳米颗粒效应．制备立方BC2N纳米复合材料将是合成新型超硬材料的新方法．

Superhard cubic BC2N compared to diamond

Recent experiments have claimed successful synthesis of cubic boron-carbonitride compounds BC_2N with an extreme hardness second only to diamond. In the present work, we examine the ideal strength of cubic BC_2N using first-principles calculations. Our results reveal that, despite the large elasticity parameters, the compositional anisotropy and strain dependent bonding character impose limitations on the strength. Consequently, the hardness of the optimal BC_2N structure is predicted to be lower than that of cubic BN, the second hardest material known. The measured extreme hardness of BC_2N nanocomposites is most likely due to the nanocrystalline size effect. These nanocomposites may point to a new method for the synthesis of new superhard materials.