Phase diagram and thermodynamic properties of the system As-Te-I

Research highlights: → The self-consistent phase diagram of the Sb-Se-I system is constructed. → Ternary phases As5Te7I, As4Te5I2 and As8Te7I5 are thermodynamically stable. → Molar thermodynamic functions of arsenic and standard integral thermodynamic functions of ternary compounds are calculated. - Abstract: The As-Te-I system has been investigated primarily by means of DTA, XRD analyses and EMF measurements with an arsenic electrode. The T-x diagram of the binary As-I system was accurately redefined and its phase diagram was constructed. A projection of the liquidus surface, an isothermal section at 300 K, and a series of polythermal sections of the phase diagram were constructed. The previously reported ternary compounds As5Te7I, As4Te5I2 and As8Te7I5 were confirmed to be equilibrium phases; the positions of phase areas with their participation were established. Areas of primary crystallization of phases, types and coordinates of the invariant equilibria on the T-x-y diagram were determined. From the X-ray powder diffraction (XRD) analysis, the crystallographic parameters of As4Te5I2 and As8Te7I5 were determined. From the EMF measurements, the partial molar functions of arsenic (ΔG-bar,ΔH-bar,ΔS-bar) as well as standard integral thermodynamic functions of ternary compounds were calculated.