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.

"Experimental study of phase equilibria and thermodynamic properties of the Tl–Se–I system" Dunya Mahammad Babanly, Ziya Saxaveddin Aliev, Vusala Asim Majidzade, Dilgam Babir Tagiyev, Mahammad Baba Babanly. "Journal of Thermal Analysis and Calorimetry", https://doi.org/10.1007/s10973-018-7677-x