Thermodynamic Study of the Ag–Sb–Se System by the EMF Method with Ag4RbI5 Solid Electrolyte

Russian Journal of Electrochemistry - The results of studying the Ag–Sb–Se system by measuring the electromotive force (EMF) of concentration cells with the Ag4RbI5 solid electrolyte...     

Phase equilibria in the Cu–Cu<Subscript>2</Subscript>Se–As system

Phase equilibria in the Cu–Cu₂Se–As were investigated by differential thermal analysis and X-ray powder diffraction analysis. Informative plots describing this system were constructed, viz., the polythermal sections Cu_0.667Se_0.333–As, Cu_0.667Se_0.333–Cu_0.735As_0.265, and Cu_0.8Se_0.2–As, the isothermal section of the phase diagram at 300 K, and the projection of the liquidus surface. The obtained results differ from the published data in length of fields of primary crystallization of phases and in coordinates of a number of invariant equilibrium points.     

Experimental Study and 3D Modeling of the Phase Diagram of the Ag–Sn–Se System

In connection with the contradictoriness of literature data, phase equilibria in the Ag–Sn–Se system were restudied by differential thermal analysis and X-ray powder diffraction analysis. A number of polythermal sections and the isothermal section at room temperature of the phase diagram were constructed, and a projection of the liquidus surface was built. The primary crystallization fields of phases and the types and coordinates of in- and monovariant equilibria were determined. It was demonstrated that, in the system, two ternary compounds, Ag₈SnSe₆ and Ag_xSn_{2 – x}Se₂ (0.84 < x < 1.06), form. The former melts congruently at 1015 K and undergoes a polymorphic transformation at 355 K, and the latter melts with decomposition by a peritectic reaction at 860 K. The formation of the compound Ag₂SnSe₃, which was previously reported in the literature, was not confirmed. Based on the phase diagrams of boundary binary systems and the results of the differential thermal analysis of a limited number of samples of the ternary system, equations were obtained for calculation and 3D modeling of the liquidus and phase-separation surfaces.     

Thermodynamic Study of the 2PbTe–AgSbTe<Subscript>2</Subscript> System Using EMF Technique with the Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> Solid Electrolyte

The work presents the results of studies of the 2PbTe–AgSbTe₂ system using the EMF technique with the Ag₄RbI₅ solid electrolyte in the temperature range of 300–430 K. Formation of a wide (0–80 mol % AgSbTe₂) region of PbTe-based solid solutions in the system is shown. Partial thermodynamic functions \(\left( {\overline {\Delta G} ,\overline {\Delta H} ,\overline {\Delta S} } \right)\) of alloyed silver are calculated on the basis of the equations of the temperature dependences of EMF. Potential-forming reactions are determined on the basis of the data on solid-phase equilibriums in the Ag₂Te–PbTe–Sb₂Te₃–Te system that are used to calculate standard thermodynamic functions of formation and standard entropies of (2PbTe) _x (AgSbTe₂)_1–x (x = 0.2; 0.4; 0.6; 08; 0.9) solid solutions.     

Thermodynamic study of the Ag-As-Se and Ag-S-I systems using the EMF method with a solid Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> electrolyte

The EMF method with a solid Ag₄RbI₅ superionic conductor was used to study the Ag-As-Se and Ag-S-I systems in the composition ranges of Ag₂Se-As₂Se₃-Se and Ag₂S-AgI-S, accordingly. Their solid-phase equilibrium diagrams are constructed or specified. The existence of ternary AgAs₃Se₅, AgAsSe₂, Ag₃AsSe₃, Ag₇AsSe₆, Ag₃SI compounds is confirmed. The standard partial and integral thermodynamic formation functions and also standard entropies were calculated for these compounds for the first time.     

Thermodynamic study of solid solutions in the SnTe–AgSbTe<Subscript>2</Subscript> system by means of EMF with solid electrolyte Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript>

The results from studying the SnTe–AgSbTe₂ system by means of EMF with the solid electrolyte Ag₄RbI₅ in the temperature range of 300–430 K are presented. The formation of a wide (≥80 mol % of AgSbTe₂) region of solid solutions based on SnTe is confirmed. Partial thermodynamic functions ΔG?, ΔH?, and ΔS? of silver in alloys are calculated from the equations for the EMF temperature dependences. Based on the literature data regarding solid-phase equilibria in the Ag₂Te–SnTe–Sb₂Te₃–Te system, potential-determining reactions are identified that allow us to calculate the standard thermodynamic formation functions and standard entropies of solid solutions (2SnTe) _x (AgSbTe₂)_1?x (х = 0.2, 0.4, 0.6, 0.8, and 0.9).     

Phase equilibria in the Cu<Subscript>2</Subscript>S–Cu<Subscript>3</Subscript>AsS<Subscript>4</Subscript>–S system

Phase equilibria in the Cu₂S–Cu₃AsS₄–S system were studied by differential thermal analysis and X-ray powder diffraction. Important plots characterizing this system were constructed, namely, the T–x diagrams of the lateral quasi-binary systems Cu₂S–Cu₃AsS₄ and Cu₃AsS₄–S, some internal sections, the isothermal section of the phase diagram at 300 K, and the projection of the liquidus surface. The fields of primary crystallization of phases and the types and coordinates of in- and monovariant equilibria were found. A wide region of separation of liquid phases was detected in the system.