Structural and optical properties of β-Si12−xCxN16 (x=0, 4, 6, 8, 12) crystals by first principles calculations

Using the density functional theory of first-principles calculations and the CASTEP module in Material Studio 5, the calculations of the structural and optical properties of the β-Si12−nCnN16 (n=0, 4, 6, 8, 12) crystals were performed. The results show that the lattice constants a, c and cell volume of the silicon carbonitride crystals become smaller, while their a/c ratio is essentially unchanged when Si atoms are continually replaced by C atoms, and these confirm they maintain isotropic shrinkage in the lattice a and c direction. The band structures of the β-Si12−nCnN16 (n=4, 6, 8) crystals are closer to β-Si12N16 rather than β-C12N16. The β-Si12N16 structure allows highest light transmission while the β-C12N16 structure allows lowest light transmission, and there is no significant difference among the light transmission for the other three structures. The absorption peaks moves to shorter wavelength side with more C replacing Si of the β-Si12N16 structure.