Phase diagrams and thermodynamic descriptions for Na–Te and K–Te binary systems

Highlights: • The associated solution model is adopted for the liquid phase. • Comprehensive comparisons between the calculated and experimentally measured data. • Important to study thermodynamic behaviors of impurity in Te-containing materials. -- Abstract: The phase diagrams and thermodynamic descriptions for the Na–Te and K–Te binary systems are explored in this work, within the CALPHAD framework. The associated solution model is adopted for the liquid phase so as to represent the abnormal behaviors for V-shaped enthalpies of mixing, abrupt changes in activity plots and sharp liquidus around certain intermetallics. Two binary associate, i.e. Na2Te and NaTe3, and two binary associates, i.e. K2Te and K2Te3, are assumed to be present in the Na–Te and K–Te melts respectively. The binary intermetallic compounds in such two binary systems, i.e. Na2Te, NaTe, NaTe3, K2Te3, KTe, K5Te3 and K2Te, are treated as stochiometric phases. Thermodynamic descriptions for such two binary systems are formulated, which allow liquidus, enthalpies of mixing, entropies of mixing, and enthalpies of formation to be well represented. This work is helpful for the construction of a Te-based thermodynamic database which can provide fundamental information for semiconductor design