Solid-phase equilibria and thermodynamic properties of the Tl2Se-As2Se3-Se system

The Tl₂Se-As₂Se₃-Se system in the equilibrium crystalline state was studied by differential thermal analysis, X-ray powder diffraction, and measurements of emf relative to a thallium electrode within the temperature range 300–400 K. An isothermal section of the phase diagram at 300 K was constructed. The formation of ternary compounds Tl₃AsSe₄, TlAsSe₂, and Tl₃AsSe₃ was confirmed, and the locations of their phase regions were determined. From the emf measurement data, the partial molar functions of thallium in alloys, the standard thermodynamic functions of formation, and the standard entropies of the above ternary compounds were calculated.