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Using first principles total energy calculations within the generalized gradient approximation (GGA), we have investigated the mechanical and thermodynamics properties of C 14-type Laves phases AMg 2 (A = Ca, Sr and Ba). Our results of equilibrium lattice parameters and formation enthalpy agree closely with previous experimental results. In particular we have discussed the thermodynamic stabilities and mechanical anisotropies of these phase structures. The polycrystalline elastic moduli have been deduced by Voigt–Reuss–Hill arithmetic approximation. Subsequently, the ductility and brittleness are characterized with the estimation from Pugh’s rule ( B / G ) and Poisson’s ratio. Additionally, the Debye temperature is calculated from the average elastic wave velocity obtained from bulk and shear moduli. The calculations of density of states and charge density difference are performed to reveal the underlying mechanism of electronic structure. Finally, variations of thermodynamic properties with temperature are predicted by calculating phonon frequencies combined within the quasi-harmonic approximation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Structural properties and electronic structure of Al2Zr and Al2Hf are studied. [•] Mechanical properties are well described and discussed. [•] The Debye temperature and anisotropic sound velocity are first assessed. [•] The bonding strength for Al–Zr bonding is stronger than that of Al–Hf bonding. [ABSTRACT FROM AUTHOR]

Abstract: The effects of pressure on the structural, electronic properties and ionic configuration of MgCu2 Laves phase were investigated by means of the first-principles method based on the density functional theory with generalized gradient approximation. The results for the equilibrium lattice constants are in good agreement with the previous experimental and other theoretical results. The elastic properties including the isotropic bulk modulus B, shear modulus G, Young modulus E and Poisson''s ratio ν of the cubic C15-type structure MgCu2 were determined by using the Voigt–Reuss–Hill averaging scheme. The results show that the MgCu2 Laves phase is ductile according to the analysis of G/B and Cauchy pressure. The Debye temperatures obtained from the elastic stiffness constants increase with increasing pressure. Finally, the pressure-dependent behavior of density of states and ionic configuration are successfully calculated and discussed. [Copyright &y& Elsevier]

The density-functional theory with the generalized gradient approximation was performed to investigate the structural properties, phase stability, electronic structure, elastic properties, and optical properties of selected Ca 5 (PO 3 ) 4 F (FA), Ca 5 (PO 3 ) 4 Cl (ClA) and Ca 5 (PO 3 ) 4 Br (BrA). Results of formation enthalpies show that FA is regarded as the most stable one in these apatites. The electronic structures including band structure, density of states and Mulliken analysis have been discussed. The predicted elastic moduli results indicate that the degree of elastic anisotropy is ordered as follows BrA > ClA > FA. By using the Clarke’s model and Cahill’s model, the thermal conductivities and the anisotropy in thermal conductivity have also been analyzed. Optic properties results indicate that the refractive indexes n for FA, ClA and BrA are 1.17, 1.19 and 1.21, respectively. [ABSTRACT FROM AUTHOR]