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.
Highlights
Mg2 X (X = Si, Ge) intermetallics have such advantages as high-temperature resistance, good corrosion resistance, high hardness, high conductivity, high-temperature electric potential and low thermal conductivity, etc.; and have important application prospects in the fields of metal matrix composite materials, structural materials, thermoelectric materials, battery materials, hydrogen storage devices, etc. [1,2,3]
525.793 that when the cell contains vacancy or anti vacancy point defects, lattice distortion occurs in the cell, Mg17Si7(MgSi)
Note that for Mg2 X (X = Si, Ge) with the same point defect structure, the Poisson’s ratio ν of the 2 × 2 × 2 supercells is smaller than that of the 1 × 1 × 2 supercells, indicating that the point defects in larger supercells can only increase the instability of transverse deformation slightly, compared with 1 × 1 × 2 supercells
Summary
The effects of strain, deformation and high pressure on the electronic, optical, and thermoelectric properties of Mg2 Si have been calculated in reference [7,8,9,10]. References [22,23,24] used the first principle to calculate the interface structure of Mg2 Si and related compounds. Kessair [25] studied the structural characteristics of seven different types of to improve thermoelectric. The effect of vacancy defect on the structure and properties of Mg2 X Elastic constant of Mg2X (X = Si, Ge) system with vacancy defect structure are calculated by Density.
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