The Cu-Te system: Phase relations determination and thermodynamic assessment

The Cu-Te binary system is of a significant interest due to the existence of Cu2Te superionic conductor in the thermoelectric application. The phase equilibria have been investigated by means of experiment and thermodynamic modeling. Based on the critical literature review on the available phase diagram and thermodynamic data, 16 crucial alloys are prepared and the phase relations in the as-cast and annealed status analyzed using X-ray diffraction (XRD) and electron probe microanalysis (EPMA). Moreover, a simultaneous differential scanning calorimetric and thermogravimetric (DSC-TG) analyses technique is utilized to confirm temperatures of invariant reactions, as well as the polymorphic transitions in the intermetallic compounds Cu2Te, Cu4Te3 and CuTe. There are five variants in the Cu2Te. A thermodynamic optimization of the Cu-Te system is then conducted with the support of the assessed literature data and the present experimental results. The liquid phase is described by the associate model due to the chemical short-range order and Cu2Te, Cu4Te3 and CuTe are treated as stoichiometric compounds in the present optimization. A set of self-consistent thermodynamic parameters are finally constructed. The present calculations are in good agreement with the available experimental data. (C) 2020 Elsevier B.V. All rights reserved.