Thermodynamic modeling of the thulium–germanium binary system

Abstract

The thulium–germanium binary system has been critically assessed by means of the CALculation of PHAse Diagram technique through Thermo-Calc software package. The thulium–germanium binary system contains nine phases based on eight compounds, the intermediate phases with no solubility ranges: Tm5Ge3, Tm5Ge4, Tm11Ge10, TmGe, Tm4Ge5, TmGe1.5, and Tm0.9Ge2 were treated as stoichiometric phases, while the compound with homogeneity range TmGe1.8 (TmGe1.8_LT and TmGe1.8_HT) was modeled using two sublattices model as (Ge,Tm)0.358(Ge)0.642. The liquid phase was modeled as substitutional solution phase, in which the excess Gibbs free energy was formulated with Redlich–Kister polynomial. The germanium (diamond_A4) and thulium (hcp_A3) were kept as pure element phases since no solubility of germanium in thulium and vice versa. The calculations based on the thermodynamic modeling agree well with the phase diagram data and few experimental thermodynamic values from the literature.