Theoretical investigation on structural and thermodynamic properties of the intermetallic compound in Mg–Zn–Ag alloy under high pressure and high temperature

Abstract

A theoretical investigation on structural and thermodynamic properties of intermetallic compounds MgAg, Mg4Zn8 and Mg4Zn4Ag8 in Mg–Zn–Ag alloy at high pressure and high temperature are performed by employing the first-principles method based on the density functional theory. The calculated values are generally speaking in good agreement with experiments and similar theoretical calculations. Theoretical calculated results indicate that intermetallic compounds MgAg, Mg4Zn8 and Mg4Zn4Ag8 are elastically stable at zero temperature and pressure. Mg4Zn8 and Mg4Zn4Ag8 are the ductility phases, and MgAg is the brittleness phase. In addition, the calculations of elastic constants and Young modulus show that the plasticity of Mg4Zn4Ag8 is the best in the three intermetallic compounds, and MgAg is the worst. Based on the quasi-harmonic Debye model, the vibrational internal energy, vibrational Helmholtz free energy, vibrational entropy, heat capacity, thermal expansion coefficient, Grüneisen parameter and Debye temperature of the intermetallic compounds in Mg–Zn–Ag alloy at high pressure and high temperature are discussed.