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

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¯,   ΔH¯,   ΔS¯) as well as standard integral thermodynamic functions of ternary compounds were calculated.

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.