A new family of sp³-hybridized carbon phases

A new family of superhard carbon allotropes C48(2i+1) is constructed by alternating even 4 and 8 membered rings. These new carbon allotropes are of a spatially antisymmetrical structure, compared with the symmetrical structures of bct-C4, Z-carbon, and P-carbon. Our calculations show that bulk moduli of C48(2i+1) are larger than that of c-BN and smaller than that of cubic-diamond. C48(2i+1) are transparent superhard materials possessing large Vicker hardness comparable to diamond. This work can help us understand the structural phase transformations of cold-compression graphite and carbon nanotubes.