tP40 carbon: A novel superhard carbon allotrope*
Heng Liu, Qingyang Fan, Fang Yang, Xinhai Yu, Wei Zhang, Sining Yun
Abstract
In this work, a novel carbon allotrope t P40 carbon with space group P 4/ mmm is proposed. The structural stability, mechanical properties, elastic anisotropy, and electronic properties of t P40 carbon are investigated systematically by using density functional theory (DFT). The calculated elastic constants and phonon dispersion spectra indicate that the t P40 phase is a metastable carbon phase with mechanical stability and dynamic stability. The B / G ratio indicates that t P40 carbon is brittle from 0 GPa to 60 GPa, while t P40 carbon is ductile from 70 GPa to 100 GPa. Additionally, the anisotropic factors and the directional dependence of the Poisson’s ratio, shear modulus, and Young’s modulus of t P40 carbon at different pressures are estimated and plotted, suggesting that the t P40 carbon is elastically anisotropic. The calculated hardness values of t P40 carbon are 44.0 GPa and 40.2 GPa obtained by using Lyakhov–Oganov’s model and Chen’s model, respectively, which means that the t P40 carbon can be considered as a superhard material. The electronic band gap within Heyd–Scuseria–Ernzerhof hybrid functional (HSE06) is 4.130 eV, and it is found that the t P40 carbon is an indirect and wider band gap semiconductor material.