A metallic superhard boron carbide: first-principles calculations

Abstract

A monoclinic BC₃ phase (denoted M-BC₃) has been predicted using first principles calculations. The M-BC₃ structure is formed by alternately stacking sequences of metallic BC-layers and insulating C atom layers, thus, the structure exhibits two-dimensional conductivity. Its stability has been confirmed by our calculations of the total energy, elastic constants, and phonon frequencies. The pressure of phase transition from graphite-like BC₃ to M-BC₃ is calculated to be 9.3 GPa, and the theoretical Vickers hardness of M-BC₃ is 43.8 GPa, this value indicates that the compound is a potentially superhard material. By comparing Raman spectral calculations of M-BC₃ and previously proposed structures with the experimental data, we speculate that the experimentally synthesized BC₃ crystal may simultaneously contain M-BC₃ and Pmma-b phases.