Monoclinic C12: A New Superhard Carbon Allotrope

Abstract

Superhard materials have always been the focus of scientific research. Based on crystal structure prediction technique combined with first-principles calculations, a new superhard carbon structure C12 (space group: C2/m) was proposed. This C12 is composed of sp2-sp3 hybrid bonding network. The calculations of mechanical properties show that it is mechanically stable and exhibits strong anisotropy. Dynamic stability of C12 at ambient pressure is confirmed by the calculation of phonon spectra. The analysis of the electronic band structure reveals that it is a narrow band gap semiconductor. Its hardness reached about 67 GPa, which means C12 is a potential superhard semiconductor material. It is expected to be used in the field of new semiconductors in the future.

Keywords: A. Superhard material, B. Carbon, C. Mechanical properties