First-principles study on the crystal, electronic structure and mechanical properties of hexagonal Al3RE (RE = La, Ce, Pr, Nd, Sm, Gd) intermetallic compounds

The structural properties, elastic properties and electronic structures of hexagonal Al3RE intermetallic compounds are calculated by using first-principles calculations based on density functional theory. Since there exists strong on-site Coulomb repulsion between the highly localized 4f electrons of RE atoms, we present a combination of the GGA and the LSDA+U approaches in order to obtain the appropriate results. The GGA calculated lattice constants for the hexagonal Al3RE intermetallic compounds are in good agreement with available experimental values. The results of cohesive energy indicate that these compounds can be stable under absolute zero Kelvin and the stability of Al3Gd is the strongest in all of the hexagonal Al3RE compounds. The densities of states for GGA and LSDA+U approaches are also obtained for the Al3RE intermetallic compounds. The mechanical properties are calculated from the GGA method in this paper. According to the computed single crystal elastic constants, Al3La, Al3Sm and Al3Gd are mechanically unstable, while Al3Ce, Al3Pr and Al3Nd are stable. The polycrystalline elastic modulus and Poisson’s ratio have been deduced by using Voigt–Reuss–Hill (VRH) approximations, and the calculated ratio of bulk modulus to shear modulus indicates that Al3La compound is ductile material, but Al3Ce, Al3Pr, Al3Nd, Al3Sm and Al3Gd are brittle materials.