Mechanical, elastic, anisotropy, and electronic properties of monoclinic phase of m-SixGe3-xN4

The structural, mechanical, elastic anisotropic, and electronic properties of the monoclinic phase of m-Si3N4, m-Si2GeN4, m-SiGe2N4, and m-Ge3N4 are systematically investigated in this work. The calculated results of lattice parameters, elastic constants and elastic moduli of m-Si3N4 and m-Ge3N4 are in good agreement with previous theoretical results. Using the Voigt-Reuss-Hill method, elastic properties such as bulk modulus B and shear modulus G are investigated. The calculated ratio of B/G and Poisson's ratio v show that only m-SiGe2N4 should belong to a ductile material in nature. In addition, m-SiGe2N4 possesses the largest anisotropic shear modulus, Young's modulus, Poisson's ratio, and percentage of elastic anisotropies for bulk modulus A(B) and shear modulus A(G), and universal anisotropic index A(U) among m-SixGe3-xN4 (x = 0, 1, 2, 3.) The results of electronic band gap reveal that m-Si3N4, m-Si2GeN4, m-SiGe2N4, and m-Ge3N4 are all direct and wide band gap semiconducting materials.