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 repo rted in the literature. Besides the solution phase (gamma) previously calle d Tl2Se but based on Tl5Se3 and the stoichiometric compound TlSe, a new pha se Tl2Se has been found to exist. Using the literature data and our experim ental results we optimized the model parameters of the Gibbs-energies of al l stable phases which resulted in an analytical description of the system. The liquid phase has been described with the association solution model, Tl Se and Tl2Se have been treated as stoichiometric while a sublattice model h as been used for the description of the gamma phase. In spite of the presen ce of two miscibility gaps in the liquid, a fair agreement was obtained bet ween experimental and calculated thermodynamic functions. (C) 1999 Elsevier Science Ltd. All rights reserved.