title: C 20 - T carbon: a novel superhard sp (3) carbon allotrope with large cavities.
abstract: Through first-principles calculations, we predict a new superhard carbon allotrope named C 20  -  T, which possesses a cubic T symmetry with space group No.198(P213). This new carbon allotrope has an all-sp (3) hybridized bonding network with 20 atoms in its primitive unit cell. The dynamic, mechanical, and thermal stabilities of this new carbon phase at zero pressure are confirmed by using a variety of state-of-the-art theoretical calculations. Interestingly, despite the fact that C 20  -  T carbon has a porous structure with large cavities, our calculations identify its superhard properties with the Vickers hardness of 72.76 Gpa. The ideal tensile and shear strength of C 20  -  T carbon are calculated to be 71.1 and 55.2 GPa respectively, comparable to that of c-BN. Electronic band calculations reveal that this new carbon allotrope is a transparent insulator with an indirect band gap of 5.44 eV. These results broaden our understanding of superhard carbon allotropes.
authors.affiliation: International Joint Research Laboratory for Quantum Functional Materials of Henan, and School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001, People's Republic of China.
authors.forename: Jia-Qi
authors.initials: JQ
authors.lastname: Wang
authors.forename: Chun-Xiang
authors.initials: CX
authors.lastname: Zhao
authors.forename: Chun-Yao
authors.initials: CY
authors.lastname: Niu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Sun
authors.forename: Yu
authors.initials: Y
authors.lastname: Jia