Search

A complete thermodynamic description of the La-Te binary system is developed by means of CALculation of PHAse Diagram (CALPHAD) method in combination with available experimental data in the literature and the present first-principles calculations based on density functional theory. The intermetallic phases with homogeneity ranges, La 3-x Te 4 and LaTe 2-x , are modeled using a two-sublattice (La,Va) 3 (Te) 4 model and a three-sublattice (La) 1 (Te) 1 (Te,Va) 1 model based on their structure features, respectively. The intermetallic phases, LaTe and LaTe 3 , are treated as stoichiometric compounds. The thermodynamic properties of the intermetallic compounds and their corresponding end members at finite temperatures are predicted using first-principles quasi-harmonic approach. The associate solution model is used to describe the short-range ordering behavior of the liquid phase. The calculated phase diagram agrees well with the available phase equilibrium data in the literature. [ABSTRACT FROM AUTHOR]

An extensive first-principles quasiharmonic phonon calculation was carried out for the thermoelectric material La 3−x Te 4 at the compositions of x = 0.0, 0.25 and 0.33, focusing at the La site vacancy effects on the thermodynamic properties. The calculated quantities include the 0 K static total energy curves and electronic band structures as well as density-of-states, the phonon density-of-states, together with the linear thermal expansion coefficients, the entropies, the enthalpies, the heat capacities, the bulk moduli, and the Debye temperature as functions of temperature up to 1200 K. Both the standard Perdew-Burke-Ernzerhof (PBE) and the Perdew-Burke-Ernzerhof revised for solids (PBEsol) exchange-correlational functionals were examined and it was found that the PBEsol functional was generally better than the PBE functional in describing both the crystal and electronic properties for the La 3−x Te 4 . [ABSTRACT FROM AUTHOR]

A complete thermodynamic description of the Yb-Ni binary system is developed by means of the CALculation of PHAse Diagram (CALPHAD) method in combination with first-principles calculations based on density functional theory (DFT) and available experimental data in the literature. Finite temperature thermodynamic properties of the Yb-Ni intermetallic compounds are predicted using the quasi-harmonic approach, where first-principles phonon calculations are performed to calculate the lattice vibrational entropy. The associate solution model is used to describe the complex thermodynamic behavior of the liquid phase. The calculated phase diagram agrees well the experimental phase equilibrium data in the literature. By the coupling of CALPHAD modeling with first-principles calculations, the present work provides a more thermodynamically accurate model of the Yb-Ni system when compared to previous models. [ABSTRACT FROM AUTHOR]

First-principles calculations have been performed to investigate the phase stability, elastic, and thermodynamic properties of Co 3 (Al,Mo,Nb) with the L1 2 structure. Calculated elastic constants show that Co 3 (Al,Mo,Nb) is mechanically stable and possesses intrinsic ductility. It is found that the shear and Young's moduli of Co 3 (Al,Mo,Nb) are smaller than those of Co 3 (Al,W). Calculated density of states indicate the existence of covalent-like bonding in Co 3 (Al,Mo,Nb). Temperature-dependent thermodynamic properties of Co 3 (Al,Mo,Nb) can be described satisfactorily using the Debye-Grüneisen approach, including entropy, enthalpy, heat capacity and linear thermal expansion coefficient, showing their significant temperature dependences. Furthermore the obtained data can be employed in the modeling of thermodynamic and mechanical properties of Co-based alloys to enable the design of high temperature alloys. [ABSTRACT FROM AUTHOR]