A new tetragonal superhard metallic carbon allotrope.

Abstract A new metallic superhard carbon allotrope C 5 with five carbon atoms per unit cell is theoretically predicted to be stable at ambient pressure through first-principles calculations combined with unbiased swarm structure searching techniques. This novel carbon allotrope consisting of a mixture of sp 2 and sp 3 carbon network exhibits excellent mechanical properties with claimed hardness of 58.5 GPa. Results from our calculated strain-stress relationship reveals that the failure mode of crystal lattice for C 5 is dominated by shear type in the (010)[101] direction with shear stress magnitude of 74.3 GPa. The calculated electronic band structure of C 5 suggests its metallic nature. Detailed analyses of band decomposed charge density show that the metallic nature is contributed by the sp 2 carbon atoms, which form conducting pathways along the a- and b -axes. Highlights • A new metallic superhard carbon allotrope C 5 is theoretically predicted. • The Vickers hardness of C 5 is 58.5 GPa. • The conducting directions are along a - and b -axes. [ABSTRACT FROM AUTHOR]