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 Cu 2 Te 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 Cu 2 Te, Cu 4 Te 3 and CuTe. There are five variants in the Cu 2 Te. 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 Cu 2 Te, Cu 4 Te 3 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. • Five variants in the Cu 2 Te are confirmed with the transition temperatures 186.7, 308.5, 352.8, 601.4 and 877.7 °C. • The homogeneity ranges of CuTe, Cu 2 Te and Cu 4 Te 3 are determined at 320 °C. • Consistent thermodynamic calculation of Cu–Te phase diagram are obtained.