First-principles study of crystal structure search, stability and mechanical property of magnesium-lithium binary system

In this paper, the energetically stable and metastable crystal structures of Mg-Li binary system are searched throughout all possible Mg concentrations by using the first-principles calculations based on density functional theory (DFT). Three stable structures are found at compositions LiMg, LiMg2 and Li2Mg3. One metastable structure is found at composition LiMg3. The formation energy, phonon spectrum, and elastic constants are calculated to evaluate the energy, dynamic and elastic stabilities, respectively. At zero temperature, both the elastic moduli (include bulk modulus B, shear modulus G, Young’s modulus E, the Poisson’s ratio ν and B/G ratio) as a function of the Mg concentration in Mg-Li binary system and the spatial direction dependences of elastic moduli are analyzed. The temperature dependents of bulk modulus and thermal expansion coefficient are also analyzed to investigate the high-temperature mechanical properties of Mg-Li binary system. With the increase of temperature, the bulk modulus of Mg-Li alloys gradually decreases and the thermal expansion coefficient gradually increases. And the calculated results also show that LiMg2 can maintain excellent mechanical strength and mechanical stability at high temperature, and has the potential of application in the high-temperature fields.