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Using first-principles calculations, we predict mechanical and thermodynamic properties of both Mg17Al12and Mg2Sn precipitates in Mg–Al–Sn alloys. The elastic properties including the polycrystalline bulk modulus, shear modulus, Young’s modulus, Lame’s coefficients and Poisson’s ratio of both Mg17Al12and Mg2Sn phases are determined with the Voigt–Reuss–Hill approximation. Our results of equilibrium lattice constants agree closely with previous experimental and other theoretical results. The ductility and brittleness of the two phases are characterized with the estimation from Cauchy pressure and the value ofB/G. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young’s modulus. The higher Debye temperature of Mg17Al12phase means that it has a higher thermal conductivity and strength of chemical bonding relative to Mg2Sn. The anisotropic sound velocities also indicate the elastic anisotropies of both phase structures. Additionally, density of states and Mulliken population analysis are performed to reveal the bonding nature of both phases. The calculations associated with phonon properties indicate the dynamical stability of both phase structures. The temperature dependences of thermodynamic properties of the two phases are predicted via the quasi-harmonic approximation. [ABSTRACT FROM PUBLISHER]

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]

Structural stability and electronic properties of polar intermetallic CaZn2and SrZn2in both CeCu2-type and MgZn2-type structures have been investigated using first-principles method. The calculated equilibrium lattice parameters agree closely with the available experimental and other theoretical results. In terms of formation enthalpy, it is discovered that the present compounds with CeCu2-type structure are energetically more stable than that with MgZn2-type. They are all mechanically stable according to the criteria of elastic stability. In particular, we have investigated the pressure effect on the compressive behaviour and structural stability of each compound. Subsequently, the bulk modulus, shear modulus, Young’s modulus, theoretical hardness, Poisson’s ratio and Debye temperature in the ground state can be estimated using Voigt–Reuss–Hill homogenization method. Mechanical anisotropy is characterized by the anisotropic factors and direction-dependent Young’s modulus. Finally, the electronic structures are determined to reveal the bonding characteristics of considered phases. [ABSTRACT FROM PUBLISHER]

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: First-principle calculations based on density functional theory are adopted to investigate the structural, electronic and thermodynamic properties of BiF3-type Mg3Gd compound. Our results for the equilibrium structural parameters are consistent with experimental values and other theoretical results. The single-crystal elastic constants, polycrystalline elastic moduli, Poisson's ratio and anisotropy factor are determined using the Voigt–Reuss–Hill approximation. Estimated Cauchy pressure and the G/B relationship indicate that Mg3Gd is mechanically stable and brittle. In addition, the electronic structure is studied within the generalized gradient approximation (GGA) and local spin density approximation (LSDA) along with Hubbard energy. The calculations associated with phonon properties confirm the dynamical stability of BiF3-type structure. Finally, the dependences of normalized volume, bulk modulus and thermodynamic properties of Mg3Gd are obtained via the quasi-harmonic Debye model. [Copyright &y& Elsevier]

Abstract: The mechanical, electronic and thermodynamic properties of L12-type Al3Sc and Al3Li precipitates have been investigated from first-principles method. The calculated equilibrium parameters such as lattice constants are in good agreement with the available experimental results and other theoretical reports. It is found that the Al3Sc exhibits a higher structural stability and stronger alloying ability than that of Al3Li since the Al3Sc possesses the lower cohesive energy and formation enthalpy. Mechanical parameters, such as the bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and universal anisotropic index A U are determined by the Voigt–Reuss–Hill approximation. In addition, the anisotropic sound velocity, Debye temperature, density of states and charge density distribution of the two precipitates are studied. The calculations associated with phonon properties confirm the dynamical stability of the L12-type structures studied. Finally, the temperature-dependent behaviors of thermodynamic properties of the two precipitates are determined within the quasi-harmonic approximation. [Copyright &y& Elsevier]

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]