Structural, elastic, and electronic properties of superhard monoclinic C32 under high pressure

Abstract

The properties of a recently proposed carbon allotrope of monoclinic C32, which is named C2/m-32 carbon, were studied by first-principles calculations. This new carbon allotrope has an all-sp3 hybridized bonding network. The dynamic and mechanical stabilities at 0 GPa and 100 GPa are demonstrated by phonon dispersion and elastic constants, respectively. Studies of the elastic anisotropy of C2/m-32 carbon show that the elastic anisotropy increases with the augment of pressure. Surprisingly, the Vickers hardness of this new carbon allotrope is 90.9 GPa, which is almost as hard as diamond. The analysis of electronic band structure shows that C2/m-32 carbon is an indirect band gap semiconductor with a band gap of 4.18 eV. These results broaden our understanding of the structural and electronic properties of carbon allotropes.