C 20 T carbon: a novel superhard sp (3) carbon allotrope with large cavities.
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.
Journal of physics. Condensed matter an Institute of Physics journal