Solid-Phase Equilibria in the SnTe–Sb2Te3–Te System and the Thermodynamic Properties of the Tin–Antimony Tellurides

The SnTe–Sb2Te3–Te system was studied in the temperature range 300–400 K by X-ray powder diffraction and EMF measurements of (–) SnTe(s.)|liquid electrolyte, Sn2+|(Sn–Sb–Te) (s) (+) reversible concentration cells. An equilibrium solid phase diagram of the system was constructed. All telluride phases of the system, namely, ternary compounds SnSb2Te4 and SnSb4Te7 and SnTe-base (α) and Sb2Te3-base (β) solid solutions, were found to be tie-lined with tellurium. Equations for temperature-dependent EMF in β + Те, β + SnSb4Te7 + Те, SnSb4Te7 + SnSb2Te4 + Те, α + SnSb2Te4 + Те, and α + Те heterogeneous phase fields were derived from EMF measurements, and were used to calculate the partial thermodynamic functions of SnTe in alloys. The thus-obtained data combined with the SnTe thermodynamic functions were used to calculate the partial molar functions of tin in alloys. The thus-obtained values and the equilibrium solid phase diagram of the SnTe–Sb2Te3–Te system, together with the relevant thermodynamic functions of Sb2Te3, were used to calculate the standard Gibbs free energies of formation and enthalpies of formation and the standard entropies of formation for SnSb2Te4, SnSb4Te7, and Sb2Te3- and SnTe-base solid solutions.