Superhard three-dimensional B3N4 with two-dimensional metallicity
Superhard three-dimensional B3N4 with two-dimensional metallicity
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具有二维金属性的超硬三维B3N4
DOI：
10.1039/c7tc00429j
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发表时间：
2017
影响因子：
6.4
通讯作者：
Zhao Zhisheng
中科院分区：
文献类型：
--
作者：
Xie Chenlong;Ma Mengdong;Liu Chao;Pan Yilong;Xiong Mei;He Julong;Gao Guoying;Yu Dongli;Xu Bo;Tian Yongjun;Zhao Zhisheng
BN作为氮化硼中的稳定化合物，无论其结构和尺寸大小，都是众所周知的绝缘体。对具有不同化学计量比的新型B-N化合物的探索可以导致发现意想不到的电气和机械性能。据我们所知，以前报道的由实验合成和理论预测得到的类石墨或类金刚石的B-N化合物大多是绝缘体或半导体。本文通过无偏群结构搜索，预测了B3N4(t-B3N4)的sp2-sp3杂化四方相(t-B3N4)在三维超强骨架中具有独特的二维金属丰度。T-B3N4的结构可以被认为是由sp2 N-N键相互连接的sp3杂化的立方BN块。值得注意的是，t-B3N4在常压下是亚稳定的，但在高压下变得稳定。层状B3N4向t-B3N4的转变压力为14.7 GPa.计算的t-B3N4相对于h-BN和N_2的生成热焓在20 GPa以上变为负值，表明t-B3N_4在压力下是可行的.用弹性常数和声子频散判据证实了它的结构稳定性。能带结构、态密度和电子轨道的分析表明，t-B3N4的金属行为主要来源于N2p电子，导电性被沿c轴堆积的绝缘硼片打断，从而导致材料的二维金属性。T-B3N4的理论维氏硬度估计为42.5 GPA，是所有建议的B3N4多晶型中最高的。此外，由于存在强的短N-N键，t-B3N4表现出超高的轴向不可压缩性，甚至超过了钻石。
As the stable compound in boron nitrides, stoichiometric BN is a well-known insulator, irrespective of its structure and dimensionality. The exploration of novel B–N compounds with various stoichiometric ratios can lead to the discovery of unexpected electrical and mechanical properties. To the best of our knowledge, previously reported graphite-like or diamond-like B–N compounds obtained from experimental synthesis and theoretical prediction are mostly insulators or semiconductors. In this paper, a sp2–sp3 hybridised tetragonal phase of B3N4 (t-B3N4) possessing unique two-dimensional (2D) metallicity in a 3D ultra-strong framework has been predicted through an unbiased swarm structure search. The structure of t-B3N4 can be considered as sp3-hybridised cubic BN blocks interlinked by sp2 N–N bonds. Noticeably, t-B3N4 is metastable at ambient pressure, but becomes stable under high pressure. The transition pressure from layered B3N4 to t-B3N4 is 14.7 GPa, and the calculated formation enthalpies of t-B3N4 with respect to h-BN and N2 become negative at pressures above 20 GPa, indicating its viability under pressure. Its structure stability has been confirmed by the criteria of both elastic constants and phonon frequency dispersions. The analyses of the band structure, density of states, and electron orbitals show that the metallic behaviour of t-B3N4 mainly originates from the N 2p electrons, and that the conduction is interrupted by the insulated boron sheets stacked along the c axis, giving rise to the 2D metallicity of the material. The theoretical Vickers hardness of t-B3N4 is estimated to reach 42.5 GPa, which is the highest among all proposed B3N4 polymorphs. Furthermore, t-B3N4 exhibits ultra-high axial incompressibility even beyond that of diamond, due to the existence of strong short N–N bonds.