First Principles Study on the Thermodynamic and Elastic Mechanical Stability of Mg2X (X = Si,Ge) Intermetallics with (anti) Vacancy Point Defects

Abstract

In this paper, based on the density functional theory, through thermodynamic and mechanical stability criteria, the crystal cell model of intermetallic compounds with vacancy and anti-site point defects is constructed and the lattice constant, formation heat, binding energy, elastic constant, and elastic modulus of Mg2X (X = Si, Ge) intermetallics with or without point defects are calculated. The results show that the difference in the atomic radius leads to the instability and distortion of crystal cells with point defects; Mg2X are easier to form vacancy defects than anti-site defects on the X (X = Si, Ge) lattice site, and form anti-site defects on the Mg lattice site. Generally, the point defect is more likely to appear at the Mg position than at the Si or Ge position. Among the four kinds of point defects, the anti-site defect x M g is the easiest to form. The structure of intermetallics without defects is more stable than that with defects, and the structure of the intermetallics with point defects at the Mg position is more stable than that at the Si/Ge position. The anti-site and vacancy defects will reduce the material’s resistance to volume deformation shear strain, and positive elastic deformation, and increase the mechanical instability of the elastic deformation of the material. Compared with the anti-site point defect, the void point defect can lead to the mechanical instability of the transverse deformation of the material and improve the plasticity of the material. The research in this paper is helpful for the analysis of the mechanical stability of the elastic deformation of Mg2X (X = Si, Ge) intermetallics under the service condition that it is easy to produce vacancy and anti-site defects.

Structural and Dielectric Properties of Ba1−xLax(Zn1/3Nb2/3)O3 Solid Solutions

“…[ 15 ] Numerically, the LaO bond energy (798 kJ mol −1 ) is larger [ 16 ] than that of BaO (140 kJ mol −1 ), [ 17 ] NbO (≈385 kJ), [ 18 ] and ZnO (211 kJ mol −1 ) [ 19 ] bond energies. Such property makes the crystallization easier which in turn reduces the defect concentrations [ 19,20 ] as observed in this study.…”

Response of Mg2X (X = Si, Ge and Sn) compounds to extreme uniaxial compression: first-principles calculations

“…Just recently, Bao et al [10] have determined the elastic and thermal properties for different structures of Mg 2 X (X = Si, Ge and Sn). Based on density functional theory (DFT), Zhao et al [15] have studied the influence of point defects on the structure and elastic mechanical stability of Mg 2 X (X = Si, Ge) intermetallic compounds.…”