Experimental study of phase equilibria and thermodynamic properties of the Tl–Se–I system
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The phase equilibria in the ternary Tl–Se–I system have been investigated by means of differential thermal analysis, X-ray powder diffraction and the electromotive force measurements (EMF) of electrochemical cells relative to the thallium electrode with ionic liquid as an electrolyte. Several polythermal sections, the isothermal section at 300 K and the projection of the liquidus surface of the system have been constructed. The homogeneity and primary crystallization regions of intermediate phases, as well as types and coordinates of non- and monovariant equilibria have been determined. Formation of two congruently melting ternary compounds (Tl5Se2I at 720 K, and Tl6SeI4 at 705 K) was observed. It was revealed that the system is characterized by the existence of wide areas of α- (based on Tl2Se) and δ-solid solutions (based on Tl5Se2I). Standard thermodynamic functions of formation and standard entropies of Tl5Se2I and Tl6SeI4 compounds were calculated based on the thermodynamic study of Tl–Se–I alloys by the EMF measurements with an ionic liquid electrolyte.
KeywordsThallium selenide–iodides Tl5Se2I Tl6SeI4 Solid solutions Phase diagram Thermodynamic properties
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