Thermodynamic and Elastic Properties of La-X (X=Al, Mg) Intermetallic Compounds from First Principles Calculations

摘要

Using first principles density functional theory (DFT) and the generalized gradient approximation (GGA), we investigate thermodynamic and elastic properties of LaAl, LaAl_2, LaAl_3, LaAl_4, La_3Al_(11), La_3Al, La_(16)Al_(13), LaMg, LaMg_2, LaMg_3, La_2Mg_(17) and La_5Mg_(41). Vibrational spectra were computed with the direct method of lattice dynamics from which OK enthalpies of formation were predicted for the known compounds. A previously unidentified low temperature monoclinic La_3Al structure is computed by following a soft mode in the phonon spectrum of the hexagonal form of La_3Al. Components of the elasticity tensor, C_(ij), are computed with a least squares fitting method using a series of symmetry unique strains and the DFT-computed stress tensor components. First principles results are compared with available experimental data.