Three-dimensional metallic carbon allotropes with superhardness

Three novel three-dimensional orthorhombic carbon phases are proposed based on first-principles calculations in this work. These phases possess dynamic stability and mechanical stability and are theoretically more favorable in energy compared to most other carbon allotropes. The hardness levels of P-C , P-C , and P-C are 47.5, 49.6, and 55.3 GPa, respectively, which are greater than those of T10, T18, and O12 carbon. In addition, although P-C , P-C , and P-C are metals, their ideal shear strengths are also greater than those of common metals such as Cu, Fe, and Al. Due to electrons crossing the Fermi level, P-C , P-C , and P-C show metallicity, and their charge densities of the band decomposition suggest that all the conductive directions of P-C , P-C , and P-C are exhibited along the - and -axis, similar to C The crystal structures of P-C , P-C , and P-C