Novel ultrahard carbon structures by cold-compressing tubes

Abstract

Four novel superhard carbon structures named L-, CM-, and K-carbon and Cco-C₁₆₀ are proposed by cold-compressing carbon nanotubes based on DFT theory, which adopt the 5 + 6 + 7, 5 + 6 + 8, 6 + 14 and 4 + 6 + 8 topological structures, respectively. The calculated phonon dispersion spectra and elastic tensors confirm the dynamic and mechanical stability of L-, CM-, and K-carbon and Cco-C₁₆₀ at ambient conditions. Owing to the unique topological structures, the four proposed phases show outstanding bulk modulus, shear modulus, Young's moduli and Vickers hardness. Except for C-diamond, the proposed Cco-C₁₆₀ is energetically more favorable than other reported carbon structures, such as M-carbon, Cco-C₈, and W-carbon. It is noteworthy that Cco-C₁₆₀ should be one of the structures in the ultrahard sp³-rich carbon polymorph that can crack diamond experimentally.