Theoretical investigation of structural, electronic and mechanical properties of the hard LaB4 material

Abstract

This study investigates the structural, electronic, elastic and dynamic properties of the lanthanum tetraboride through Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT), using the Generalized Gradient Approximation (GGA), Local Density Approximation (LDA) and Local Density Approximation plus Hubbard (LDA + U) exchange-correlation potentials. The obtained lattice constants and atomic positions are in good agreement with the available data presented in literature. The band structure illustrated that LaB4 is a conductor and the partial density of states and electronic localization function (ELF) analysis indicated the existence of covalent character in B–B and B–La bonds, which indicate that this material is an intermetallic in nature. We discussed the physical significance of the obtained elastic constants, stress-strain relations and the other relevant quantities, such as shear, bulk and Young's moduli, Poisson's ratio, hardness, and Debye temperature. The results revealed that the lanthanum tetraboride is mechanically stable, brittle, hard and anisotropic. Finally, we estimated the thermodynamic properties such as the Helmholtz free energy, internal energy, entropy and specific heat capacity in the 0–2000 K temperature range, within the phonon-dispersion and the phonon density of states curves.