Solid-Phase Equilibria in the SnTe–Sb 2 Te 3 –Te System and the Thermodynamic Properties of the Tin–Antimony Tellurides

The SnTe–Sb 2 Te 3 –Te system was studied in the temperature range 300–400 K by X-ray powder diffraction and EMF measurements of (–) SnTe(s.)|liquid electrolyte, Sn 2+ |(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 SnSb 2 Te 4 and SnSb 4 Te 7 and SnTe-base (α) and Sb 2 Te 3 -base (β) solid solutions, were found to be tie-lined with tellurium. Equations for temperature-dependent EMF in β + Те, β + SnSb 4 Te 7 + Те, SnSb 4 Te 7 + SnSb 2 Te 4 + Те, α + SnSb 2 Te 4 + 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–Sb 2 Te 3 –Te system, together with the relevant thermodynamic functions of Sb 2 Te 3 , were used to calculate the standard Gibbs free energies of formation and enthalpies of formation and the standard entropies of formation for SnSb 2 Te 4 , SnSb 4 Te 7 , and Sb 2 Te 3 - and SnTe-base solid solutions.