Predictions of mechanical and thermodynamic properties of Mg17Al12 and Mg2Sn from first-principles calculations

Using first-principles calculations, we predict mechanical and thermodynamic properties of both Mg17Al12 and Mg2Sn precipitates in Mg-Al-Sn alloys. The elastic properties including the polycrystalline bulk modulus, shear modulus, Young's modulus, Lame's coefficients and Poisson's ratio of both Mg17Al12 and Mg2Sn phases are determined with the Voigt-Reuss-Hill approximation. Our results of equilibrium lattice constants agree closely with previous experimental and other theoretical results. The ductility and brittleness of the two phases are characterized with the estimation from Cauchy pressure and the value of B/G. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young's modulus. The higher Debye temperature of Mg17Al12 phase means that it has a higher thermal conductivity and strength of chemical bonding relative to Mg2Sn. The anisotropic sound velocities also indicate the elastic anisotropies of both phase structures. Additionally, density of states and Mulliken population analysis are performed to reveal the bonding nature of both phases. The calculations associated with phonon properties indicate the dynamical stability of both phase structures. The temperature dependences of thermodynamic properties of the two phases are predicted via the quasi-harmonic approximation.