Structure, mechanical stability, lattice dynamics and thermodynamic properties of C15-Laves phase Mg2Ce

Abstract

A systematic study of the structure, mechanical properties, lattice dynamics and thermo-physical properties of C15-Laves phase Mg2Ce is performed through density functional theory (DFT) and density functional perturbation theory (DFPT). The optimized equilibrium lattice constant, equilibrium cell volume, bulk modulus and its pressure derivative reproduce perfectly the available experimental data and other calculated values. The individual crystal elastic constants and polycrystalline aggregates including the isotropic bulk modulus, shear modulus, Young's modulus, brittle/ductile characteristics, Poisson's ratio, Debye temperature and the integration of elastic wave velocities over different directions for C15-Laves phase Mg2Ce have also been evaluated up to 15 GPa using “energy-strain” method, the results indicate that C15–Mg2Ce is mechanically stable up to 15 GPa. Ideal tensile strengths (ITS) along three typical crystallographic orientations, and ideal shear strengths (ISS) in the (010)[101] slip direction of Mg2Ce have been explored by virtue of first principles total energy method. Additionally, both the density functional perturbation theory and the small displacement method are applied to determine the lattice dynamical stability and vibrational modes of Mg2Ce, it is predicted that C15-Laves Mg2Ce system is also dynamically stable up to 15 GPa. The microscopic symmetry properties of optical modes of Mg2Ce at the center of the Brillouin zone have also been analyzed with the combination of group theory. Numerous thermodynamic quantities in the temperature range 0–1000 K and the pressure range 0–15 GPa are obtained further based on quasi-harmonic approximation (QHA) and Debye model.