title: Cubic gauche-CN: A superhard metallic compound predicted via first-principles calculations.
abstract: In this paper, we suggest a novel potential superhard material, a new carbon nitride phase consisted of sp(3) hybridized bonds, possessing a cubic P2(1)3 symmetry (8 atoms/cell, labeled by cg-CN) which is similar to cubic gauche nitrogen (cg-N) by first-principles calculations. It is a metallic compound, while most of other superhard materials are insulators or semiconductors. The Vickers hardness of cg-CN is 82.56 GPa, and if we considered the negative effect of metallic component on hardness, it is 54.7 GPa, which is much harder than any other metallic materials. It is found that a three-dimensional C-N network is mainly responsible for the high hardness. Both elastic constant and phonon-dispersion calculations show that this structure remains mechanically and dynamically stable in the pressure ranges from 0 to 100 GPa. Furthermore, we compared our results with many other proposed structures of carbon nitride with 1:1 stoichiometry and found that only cg-CN is the most favorable stable crystal structure. Formation enthalpies calculations demonstrate that this material can be synthesizable at high pressure (12.7-36.4 GPa).
authors.affiliation: State Key Lab of Superhard Materials, College of Physics, Jilin University, People's Republic of China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Wang
authors.forename: Kuo
authors.initials: K
authors.lastname: Bao
authors.forename: Fubo
authors.initials: F
authors.lastname: Tian
authors.forename: Xing
authors.initials: X
authors.lastname: Meng
authors.forename: Changbo
authors.initials: C
authors.lastname: Chen
authors.forename: Bowu
authors.initials: B
authors.lastname: Dong
authors.forename: Da
authors.initials: D
authors.lastname: Li
authors.forename: Bingbing
authors.initials: B
authors.lastname: Liu
authors.forename: Tian
authors.initials: T
authors.lastname: Cui