Mechanical Properties and Electronic Structures of M (M=Ti, V, Cr, Mn and Fe) Doped β-Si₃N₄ from First-Principle

The structures, mechanical properties and electronic structures of M metals (M=Ti, V, Cr, Mn and Fe) doped β-Si₃N₄ were investigated by First-principles calculations within CASTEP. The calculated lattice parameters of β-Si₃N₄ were consistent with previous date. The cohesive energy and formation enthalpy show that initial β-Si₃N₄ has the highest structural stability. The calculated elastic constant and the Voigt-Reuss-Hill approximation indicate that elastic moduli of β-Si₃N₄ are slightly reduced by M doping. Based on Poisson’s and Pugh’s ratio, β-Si₃N₄ is a ductile material and the toughness of β-Si₃N₄ increases with M doping, and Fe doping exhibited the best toughness. The results of density of states, charge distributions and overlapping populations indicate that β-Si₃N₄ has the strong covalent and ionic bond strength between N and Si.