First-principles calculation on the structure stability, elastic properties and electronic structure of P-doped Mg2Si

In this study, the effect on the structure stability, elastic properties and electronic structure of P-doped Mg2Si were studied by the first-principles pseudopotential plane wave method based on density functional theory. The lattice constants, formation enthalpy, cohesive energy, elastic constants, and elastic moduli of Mg2Si, Mg7Si4P, Mg8Si3P and Mg8Si4P were calculated, and the electronic structure analysis was also performed. The occupation tendency, structural stability, bonding characteristics, orbital hybridization and the change of conductivity of doping P atoms in the matrix were further investigated. Among them, the research results of formation enthalpy, cohesive energy and elastic constant show that Mg2Si, Mg8Si3P and Mg8Si4P can all exist stably in the system, and the crystal structure of Mg7Si4P can not exist stably. P atoms doping into the Mg2Si lattice tend to occupy Si atoms position preferentially. The results of elastic modulus study show that Mg2Si and Mg8Si4P are brittle phase and Mg8Si3P is ductile phase. The plasticity and toughness of Mg2Si alloy system are improved by doping P atoms. The electronic structure analysis shows that the method of doping P atoms changes the orbital hybridization and bonding characteristics of the system. The Mg-P and Si-P covalent bond formed by Mg8Si3P and Mg8Si4P increase the structure stability. The energy band structure analysis also show reduction of the band gap from 0.224 to 0.184 eV for Mg2Si with P dopants at the substitutional Si-sites and the band gap closure in the system with interstitial P-impurities. It enhances the metallic property of the material, and Mg8Si4P phase also transform from its semiconducting to metallic state. Consequently, this method both increases the carrier concentration and reduces the energy of free electron transition. The conductivity of the Mg2Si alloy system will be improve.