Thermodynamic assessments of the Yb-Bi and the Yb-Te systems

The Yb-Bi and the Yb-Te systems are thermodynamically assessed by CALPHAD approach based on the available experimental data including thermochemical properties and phase equilibria. All of the intermetallic phases in these two systems are treated as stoichiometric compounds due to their unnoticeable homogeneity ranges, and their formation enthalpies at 0 K are calculated by the first-principles method to supplement the thermochemical property data for the present optimization. The values of the first-principles calculation are confirmed by the lattice constants and the equilibrium modulus of the compounds available from experiments. Given the asymmetric shapes of the liquidus around the compounds Yb4Bi3/YbTe in the Yb-Bi/Te phase diagrams, both the associate model and the sub-regular solution model are used to describe the Gibbs free energy of the liquid phase for the two systems. The comparison between the optimization results and the experimental data for the Yb-Bi/Te systems shows that a much better agreement is obtained by means of the associate model than the sub-regular solution model.