Physical Properties of C-Si Alloys in C2/m Structure

Using the first principles calculations based on density functional theory, the crystal structure, elastic anisotropy, and electronic properties of carbon, silicon and their alloys (C-12 Si-4, C8Si8, and C-4 Si-12 ) in a monoclinic structure (C2/m) are investigated. The calculated results such as lattice parameters, elastic constants, bulk modulus, and shear modulus of C-16 and Si-16 in C2/m structure are in good accord with previous work. The elastic constants show that C-16, Si-16, and their alloys in C2/m structure are mechanically stable. The calculated results of universal anisotropy index, compression and shear anisotropy percent factors indicate that C-Si alloys present elastic anisotropy, and C8Si8 shows a greater anisotropy. The Poisson's ratio and the B/G value show that C8Si8 is ductile material and other four C-Si alloys are brittle materials. In addition, Debye temperature and average sound velocity are predicted utilizing elastic modulus and density of C-Si alloys. The band structure and the partial density of states imply that C-16 and Si-16 are indirect band gap semiconductors, while C12Si4, C8Si8, and C4Si12 are semi-metallic alloys.