Phase diagram experimental investigation and thermodynamic assessment of the thallium–selenium system

The Tl–Se system was investigated by DSC and X-ray diffraction measurements to clarify the contradictory information concerning the phase diagram reported in the literature. Besides the solution phase (γ) previously called Tl2Se but based on Tl5Se3 and the stoichiometric compound TlSe, a new phase Tl2Se has been found to exist. Using the literature data and our experimental results we optimized the model parameters of the Gibbs-energies of all stable phases which resulted in an analytical description of the system. The liquid phase has been described with the association solution model, TlSe and Tl2Se have been treated as stoichiometric while a sublattice model has been used for the description of the γ phase. In spite of the presence of two miscibility gaps in the liquid, a fair agreement was obtained between experimental and calculated thermodynamic functions.