Thermodynamic assessment of the Ytterbium–Germanium binary system

Abstract

The Ytterbium–Germanium binary system was evaluated using the CALPHAD method through Thermo-Calc software package; the thermodynamic parameters involved in the Gibbs free energy models of the phases are optimized based on all available literature experimental data including the phase equilibria information and few thermodynamic measurements. The Ytterbium–Germanium system contain six intermetallic compounds Yb2Ge, Yb5Ge3, Yb5Ge4, Yb11Ge10, Yb3Ge5, and Yb3Ge8, which are all treated as stoichiometric phases. The excess term of the Gibbs free energy of the liquid phase was assessed with the recent exponential temperature dependence of the interaction energies by Kaptay and compared with the linear temperature dependence of Redlich–Kister polynomial equation results. The Germanium (Diamond_A4) and the two allotropic transformations of Ytterbium: βYb (fcc_A1) and γYb (bcc_A2), were kept as pure element phases since no solubility of Germanium in Ytterbium and vice versa. A reasonable agreement between the calculated results (the phase diagram and model parameters) and literature data was obtained for this system. The optimization process allows us to accomplish the results which are reported in a series of figures and tables.