Design and physical property study of seven novel carbon allotropes by Random methods combined group and Graph theories

Abstract

Carbon materials are important semiconductor materials. For enriching the structure of carbon materials, the eight novel carbons with R-3m phase are predicted by using Random methods based on Group and Graph theories. Among these allotropes, one (R-3m/C−8(-|-)) was excluded through stability criterion, and the others new carbon structures meet all stability conditions, including thermal stability, dynamical stability, mechanical stability, and thermodynamic stability. According to two empirical hardness model criteria, all the hardness of seven novel carbon allotropes are above 50 GPa. Particularly, R-3m/C, R-3m/C−2(-|-), R-3m/C−3(-|-), R-3m/C−6(-|-), and/R−3(-|-)m/C−7(-|-) belong to superhard materials. Electronic band structures of these materials are demonstrated by HSE06 hybrid functional, where R-3m/C, R-3m/C−2(-|-), R-3m/C−3(-|-), R-3m/C−4(-|-), R-3m/C−6(-|-), and/R−3(-|-)m/C−7(-|-) are wide band gap semiconductors, while R-3m/C, R-3m/C−2(-|-) are quasi-direct band gap structures. The R-3m/C−4(-|-) exhibits the greatest elastic anisotropy in elastic modulus. There materials with different crystalline phase structures are characterized by using X-ray diffraction spectroscopy. Here, the predicted new allotropes with excellent physical properties provide theoretical guidance for further development and expansion of carbon material applications.