Zhang Xinxin, Zhao Yu, Zhang Miao, Liu Hanyu, Yao Yansun, Cheng Taimin, Chen Hui
Department of Science, Shenyang University of Chemical Technology, Shenyang 110142, People's Republic of China.
J Phys Condens Matter. 2017 Nov 15;29(45):455401. doi: 10.1088/1361-648X/aa8a08.
Boron carbide (BC) is one of the hardest materials known to date. The extreme hardness of BC arises from architecturally efficient B or BC icosahedrons and strong inter-icosahedral B-C bonding. As an excellent material for use in ballistic armor, the mechanic limit of BC and possible phase transitions under extreme stress conditions are of great interest. Here we systematically explored the post-icosahedral solid structures of BC under high pressure, using an unbiased structure search method. A new structure composed of extended framework of B and zigzag chains of C is predicted to be stable above 96 GPa. The new structure was predicted to have a high Vickers hardness of 55 GPa and simultaneously to retain a metallic ground state. The exceptional mechanical properties found in this structure are attributed to strong sp covalent network formed under extreme pressure conditions. The predicted structure represents a new type of superhard boron carbides that form under high pressure without the presence of boron icosahedrons, which encourages experimental exploration in this direction.
碳化硼（BC）是迄今为止已知的最硬材料之一。碳化硼的极高硬度源于结构高效的B或BC二十面体以及二十面体间强大的B - C键。作为用于防弹装甲的优良材料，碳化硼的力学极限以及在极端应力条件下可能发生的相变备受关注。在此，我们使用无偏结构搜索方法系统地探索了高压下碳化硼的二十面体后固体结构。预测一种由B的扩展框架和C的锯齿链组成的新结构在96吉帕以上是稳定的。该新结构预计具有55吉帕的高维氏硬度，同时保持金属基态。在这种结构中发现的优异力学性能归因于在极端压力条件下形成的强大sp共价网络。预测的结构代表了一种新型的超硬碳化硼，它在高压下形成且不存在硼二十面体，这鼓励了在这个方向上的实验探索。
