542 / 2019-03-20 11:38:23

Superhard three-dimensional B2C3N2 with two-dimensional metallicity

B-C-N compounds; superhard; 2D metallicity

全体主题 > High Pressure Physics and Materials Science

Superhard three-dimensional B2C3N2 with two-dimensional metallicity
Baozhong Li, Chenlong Xie, Kun Luo, Mengdong Ma, Yufei Gao, Yang Zhang, Yongjun Tian and Zhisheng Zhao*
Center for High Pressure Science, State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
*Email: zzhao@ysu.edu.cn
Considerable efforts have been devoted to search for new superhard materials as they play a very important role in the development of modern science and technology. Ternary boron carbon nitrogen (B-C-N) compounds with extremely high hardness and great thermal and chemical stability have drawn a great attention in decades. Moreover, B-C-N compounds are expected to produce electronic devices because their band gap can be regulated by the atomic composition or arrangement. A novel B-C-N compound with unique electronic and mechanical properties is desirable.
It is known that graphite and hexagonal BN can be transformed into a denser structure in high pressure and high temperature conditions. Experimentally, graphene-like B2C3N2 nanopans have been synthesized by Kumar et al.. It may be possible that a new high-pressure B2C3N2 phase could be synthesized from graphene-like B2C3N2 phase under high pressure and high temperature. B2C3N2 compounds with excellent mechanical and electrical properties in 3D structures arise our interest.
In this study, we predicted a sp2-sp3 hybrid tetragonal phase of B2C3N2 (t-B2C3N2) with distinctive two-dimensional (2D) metallicity in a 3D ultra-strong framework through the particle swarm optimization (PSO) technique as implemented in the CALYPSO code. This I-4m2 structure has a density of 3.17 g/cm3 with 14 atoms per unit cell. The stability of t-B2C3N2 has been confirmed by the criterions of elastic constants and phonon frequency dispersions. The theoretical Vickers hardness of t-B2C3N2 is estimated to about 40 GPa according to the Chen’s formula, indicating it is a potential superhard material. After the analyses of band structure and density of states, the metallic behaviour of t-B2C3N2 is mainly originated from the 2p electrons of the N and C1 atomic layers, and the conduction is interrupted by the insulated C2 atomic layers stacked along c axis, exhibiting its 2D metallicity on the ab planes. The t-B2C3N2 with such unique properties can be used as electronic devices.

Keywords: B-C-N compounds; superhard; 2D metallicity