Electronic, optical and mechanical properties of a novel high-symmetry silicon carbide predicted using first-principles calculations

Based on the first-principles method of density functional theory, a new type of silicon carbidewith a highly symmetrical truncated octahedron structure is studied, named Pm3n-SiC. This silicon carbide structure belongs to the ​​cubic crystal system​​ with a ​​lattice parameter of 5.335 Å​​. Its unit cell comprises 8 regular hexagons and 6 squares, exhibits a carbon-silicon bond length of 1.886 Å, and belongs to the Pm3n symmetry group. The results show that Pm3n-SiC has a formation enthalpy of -0.321 eV. Its phonon dispersion spectrum exhibits no imaginary frequencies, and its independent elastic constants satisfy the mechanical stability criteria. This indicates that Pm3n-SiC is readily synthesizable and exhibits both dynamic and mechanical stability.​ According to Chen's model, the Vickers hardness is estimated to be about 16.3GPa, and the universal elastic anisotropy index A ^U = 0.57, which is a medium-hardness anisotropic material. The density of states of Pm3n-SiC is similar to that of conventional SiC, in which the Si-3p orbital dominates the conduction bands. The C-2p orbital and the Si-3p orbital strongly hybridize the dominant valence bands. The analysis of optical properties shows that the predicted new silicon carbide (Pm3n-SiC) has a strong absorption capacity for ultraviolet light and extreme ultraviolet light