Physical Properties of C-Si Alloys in C2/m Structure**Supported by the Natural Science Foundation of China under Grant No. 61474089, Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics under Grant No. 2015-0214. YY.K

Abstract

Using the first principles calculations based on density functional theory, the crystal structure, elastic anisotropy, and electronic properties of carbon, silicon and their alloys (C12Si4, C8Si8, and C4Si12) in a monoclinic structure (C2/m) are investigated. The calculated results such as lattice parameters, elastic constants, bulk modulus, and shear modulus of C16 and Si16 in C2/m structure are in good accord with previous work. The elastic constants show that C16, Si16, 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 C16 and Si16 are indirect band gap semiconductors, while C12Si4, C8Si8, and C4Si12 are semi-metallic alloys.