title: A metallic superhard boron carbide: first-principles calculations.
abstract: A monoclinic BC3 phase (denoted M-BC3) has been predicted using first principles calculations. The M-BC3 structure is formed by alternately stacking sequences of metallic BC-layers and insulating C atom layers, thus, the structure exhibits two-dimensional conductivity. Its stability has been confirmed by our calculations of the total energy, elastic constants, and phonon frequencies. The pressure of phase transition from graphite-like BC3 to M-BC3 is calculated to be 9.3 GPa, and the theoretical Vickers hardness of M-BC3 is 43.8 GPa, this value indicates that the compound is a potentially superhard material. By comparing Raman spectral calculations of M-BC3 and previously proposed structures with the experimental data, we speculate that the experimentally synthesized BC3 crystal may simultaneously contain M-BC3 and Pmma-b phases.
authors.affiliation: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, Hebei Province, China. hjl@ysu.edu.cn.
authors.forename: Mengdong
authors.initials: M
authors.lastname: Ma
authors.forename: Bingchao
authors.initials: B
authors.lastname: Yang
authors.forename: Zihe
authors.initials: Z
authors.lastname: Li
authors.forename: Meng
authors.initials: M
authors.lastname: Hu
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Wang
authors.forename: Lin
authors.initials: L
authors.lastname: Cui
authors.forename: Dongli
authors.initials: D
authors.lastname: Yu
authors.forename: Julong
authors.initials: J
authors.lastname: He