Phase relations in PbSe-PbTe alloys of the Ag-Pb-Se-Te system studied by EMF measurements

The emf ( E ) of Ag | AgI | Ag 2 GeS 3 glass | D galvanic cells (where Ag and D are the electrodes of the cell, D is a three- or four-phase equilibrium alloy of the Ag-Pb-Se-Te system, and AgI | Ag 2 GeS 3 glass is a bilayer membrane with purely ionic (Ag + ) conductivity) was measured as a function of temperature in the range 520–575 K. The E ( T ) data were used to calculate the thermodynamic functions of saturated solid solutions in the PbSe-PbTe section of the Ag-Pb-Se-Te system. The observed breaks in the composition dependences of Δ f G 298 0 , Δ f H 298 0 , and T Δ r S 298 0 and the change in the sign of T Δ r S 298 0 in the range PbSe 0.7 Te 0.3 -PbSe 0.73 Te 0.27 are interpreted as evidence for the formation of an intermediate berthollide phase.