Mechanical and thermodynamics properties of Al2Ca and Mg2Ca under various pressure: A first principle study

Abstract

The mechanical and thermodynamic properties of Al2Ca and Mg2Ca in the pressure range of 0~100 Gpa were investigated using first-principles calculations. The structural parameters, such as lattice constant ratio, unit cell volume ratio, density, were investigated. The calculated elastic constants satisfy the born’s stability criterion, indicating that they are mechanically stable at normal and high pressure. Mechanical parameters such as bulk modulus, shear modulus, and Young’s modulus of polycrystalline materials have been derived from single-crystal elastic constants. The Poisson’s ratio and anisotropy were investigated. The results show that the B/G value of Mg2Ca is greater than 1.75, indicating it is a ductile phase under various pressures. When the pressure was equal to 40 Gpa, Al2Ca was transferred brittle to toughness, and the bulk modulus, shear modulus, and Young’s modulus of Al2Ca were all larger than those of Mg2Ca, indicating that the comprehensive mechanical properties of Al2Ca are better than those of Mg2Ca. The constant heat capacity obtained by the quasi-harmonic approximation indicates that the ability of Mg2Ca to release or store heat is greater than that of Al2Ca. Moreover, the coefficient of thermal expansion (α) increases exponentially at lower temperatures and linearly at higher temperatures for both alloys.