Thermodynamic Modeling of the Pt-Te and Pt-Sb-Te Systems

The Pt-Te and the Pt-Sb-Te systems are modeled using the calculation of phase diagram (CALPHAD) technique. In the Pt-Te system, the liquid phase is modeled as (Pt, PtTe₂, Te) using the associate model, and four intermediates, PtTe₂, Pt₂Te₃, Pt₃Te₄ and PtTe, are treated as stoichiometric compounds and their enthalpies of formation are obtained by means of first-principles calculations. The solution phases, fcc(Pt) and hex(Te), are described as substitutional solutions. Combined with the thermodynamic models of the liquid phase in the Pt-Sb and Sb-Te systems in the literature, the liquid phase of the Pt-Sb-Te ternary system is modeled as (Pt, Sb, Te, Sb₂Te₃, PtTe₂) also using the associate model. The compounds, PtTe₂, Pt₂Te₃, Pt₃Te₄ and PtTe in the Pt-Te system and PtSb₂, PtSb, Pt₃Sb₂ and Pt₇Sb in the Pt-Sb system are treated as line compounds Pt_m(Sb,Te)_n in the Pt-Sb-Te system, and the compound Pt₅Sb is treated as (Pt,Sb)₅(Pt,Sb,Te). A set of self-consistent thermodynamic parameters is obtained. Using these thermodynamic parameters, the experimental Pt-Te phase diagram, the experimental heat capacities of PtTe and PtTe₂, the enthalpies of formation from first-principles calculations for PtTe₂, Pt₂Te₃, Pt₃Te₄, and PtTe, and the ternary isothermal sections at 873 K, 923 K, 1073 K and 1273 K are well reproduced.