Thermodynamic study of the Cu-As-S system by EMF measurements with Cu<Subscript>4</Subscript>RbCl<Subscript>3</Subscript>I<Subscript>2</Subscript> as a solid electrolyte

The Cu-As-S system has been studied at temperatures from 300 to 370 K using emf measurements with Cu₄RbCl₃I₂ as a Cu⁺ ion conducting solid electrolyte, and its subsolidus phase diagram has been mapped out, including the ternary compounds Cu₃AsS₄, Cu₆As₄S₉, Cu₄As₂S₅, Cu₃AsS₃, and CuAsS. From the emf data, we have calculated the partial molar thermodynamic functions (D[`(G)]\Delta \bar G, D[`(H)]\Delta \bar H, and D[`(S)]\Delta \bar S) of the copper in the alloys and the standard thermodynamic functions of formation and standard entropies of the ternary compounds.     

Phase Equilibria in the Cu<Subscript>2</Subscript>Se–Cu<Subscript>3</Subscript>AsSe<Subscript>4</Subscript>–Se System and Thermodynamic Properties of Cu<Subscript>3</Subscript>AsSe<Subscript>4</Subscript>

The Cu₂Se–Cu₃AsSe₄–Se system has been studied using differential thermal analysis, X-ray diffraction, and emf measurements on concentration cells using Cu₄RbCl₃I₂ as a solid electrolyte. We have constructed a number of vertical sections through the phase diagram, the room-temperature solid-state phase compatibility diagram, and a projection of the liquidus surface. The primary crystallization fields of the phases present and the types and coordinates of in- and univariant equilibria in the system have been identified. The system has been shown to contain a broad liquid–liquid immiscibility region. Using emf data, we evaluated the standard thermodynamic functions of formation and standard entropy of the Cu₃AsSe₄ compound.     

Thermodynamic properties of copper thallium tellurides

The Cu-Tl-Te system has been studied in the composition region Cu-CuTe-Cu₂TlTe₂ using emf measurements on reversible concentration cells relative to a thallium electrode. The partial subsolidus phase diagram inferred from the emf data includes the ternary compounds Cu₉TlTe₅, Cu₃TlTe₂, and Cu₂TlTe₂. The emf data were used to evaluate the relative partial thermodynamic functions ($ \Delta \bar G $ \Delta \bar G , $ \Delta \bar H $ \Delta \bar H and $ \Delta \bar S $ \Delta \bar S ) of the thallium in the alloys. From the subsolidus phase diagram, we identified the potential-determining reactions responsible for these functions and calculated the standard thermodynamic functions of formation and standard entropies of the ternary compounds Cu₉TlTe₅ (−Δ_f G ⁰(298 K) = 244.0 ± 2.4 kJ/mol, −Δ_f H ⁰(298 K) = 241 ± 14 kJ/mol, S ⁰(298 K) = 621 ± 7 J/(mol K)), Cu₃TlTe₂ (117.1 ± 1.2, 117 ± 5, 264 ± 4), and Cu₂TlTe₂ (94.8 ± 0.9, 92 ± 7, 237 ± 3).     

Solid-state equilibria and thermodynamic properties of compounds in the Bi-Te-I system

The Bi-Te-I system has been studied by differential thermal analysis, x-ray diffraction, and emf measurements in the temperature range 300–400 K using concentration cells of the type (?)Bi(s) | glycerol + KI + BiI₃ | Bi-Te-I(s)(+). The results have been used to construct the 300-K section of the Bi-Te-I phase diagram. The existence of the ternary compounds BiTeI, Bi₂TeI, and Bi₄TeI_1.25 has been confirmed, and the position of the phase fields involving these compounds has been accurately determined. Using emf data, we have evaluated the partial thermodynamic functions (Δ\(\bar G\), Δ\(\bar H\), and Δ\(\bar S\)) of the bismuth in the alloys studied, the standard thermodynamic functions of formation of the ternary compounds, and their standard entropies.     

Thermodynamic properties of arsenic sulfides studied by EMF measurements

The solid-state phase equilibria and thermodynamic properties of alloys in the As-S system have been studied using emf measurements. The temperature and composition dependences of the emf confirm the existence of As₂S₅, As₂S₃, AsS, and As₄S₃ with narrow homogeneity ranges. The emf data are used to calculate relative partial molar functions of the As in the alloys and the standard Gibbs energies and standard entropies of the arsenic sulfides.     

Solid-state phase equilibria and thermodynamic properties of ternary compounds in the Tl-Sb-S system

The Tl-Sb-S system has been studied in the composition region Tl₂S-Sb₂S₃-S using differential thermal analysis, X-ray diffraction, and emf measurements on thallium concentration cells at temperatures from 300 to 390 K, and the 300-K isothermal section of its phase diagram has been mapped out. The existence of the ternary compounds TlSb₅S₈, TlSb₃S₅, TlSbS₃, TlSbS₂, Tl₃SbS₄, and Tl₃SbS₃ has been confirmed, and the position of the phase fields involving these compounds has been accurately determined. Using emf data, we have evaluated the partial molar functions (D[`(G)]\Delta \bar G , D[`(H)]\Delta \bar H , D[`(S)]\Delta \bar S ) of the thallium in the alloys studied, the standard thermodynamic functions of formation of the ternary compounds, and their standard entropies.     

Influence of the nature and density of defects on the thermodynamic and electrical properties of semiconductor materials

This paper examines the use of coulometric titration in studies of the nonstoichiometry, defect structure, and thermodynamic properties of semiconductor materials and also for doping of a number of chalcogenides with lead, copper, and germanium. A direct relationship is established between the thermodynamic and electrical properties of the binary compound semiconductors Pb_{1 ± δ}X (X = S, Se, Te), Cu_{2 ± δ}Se, and Cd_{2 ± δ}Se and the ternary spinel semiconductors Cd_{1 ? δ}Cr₂Se₄ and Cu_{1 ± δ}Cr₂S₄ within their homogeneity ranges. The width and symmetry of the homogeneity range of these semiconductor materials are determined using coulometric titration in combination with emf and electrical conductivity measurements. Electrochemically doped nonstoichiometric copper selenide samples are shown to have compositions in the range Cu_1.27Se–Cu_2.73Se.     

Composition range and thermodynamic properties of Tl<Subscript>5</Subscript>Se<Subscript>2</Subscript>Br-based solid solutions

The equilibrium subsolidus phase diagram of the TlBr-Tl₂Se-TlSe system has been mapped out using X-ray diffraction analysis and emf measurements on thallium concentration cells. Tl₅Se₂Br has been shown to have a broad homogeneity region. The emf results are used to evaluate the relative partial thermodynamic functions of the thallium in the alloys studied and the standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰(298 K), S ⁰(298 K)) of the Tl₅Se₂Br-based solid solutions.     

Thermodynamic study of the Ag2S-As2S3-S system by EMF measurements with Ag4RbI5 as a solid electrolyte

The Ag-As-S system has been studied in the composition region Ag₂S-As₂S₃-S at temperatures from 300 to 380 K using emf measurements with Ag₄RbI₅ as a Ag⁺ ion conducting solid electrolyte, and its subsolidus phase diagram has been mapped out, including the ternary compounds AgAsS₂, Ag₃AsS₃, and Ag₇AsS₆. From the emf data, we have calculated the partial molar thermodynamic functions $\left( {\left( {\Delta \bar G,\Delta \bar H,\Delta \bar S} \right)} \right)$ of the silver in the three-phase regions AgAsS₂ + As₂S₅ + As₂S₃, Ag₃AsS₃ + AgAsS₂ + S, and Ag₇AsS₆ + Ag₃AsS₃ + S, which were then used to evaluate the standard thermodynamic functions of formation and standard entropies of the ternary compounds by the method of potential-determining reactions.     

Thermodynamic properties of the SnSb<Subscript>2</Subscript>Te<Subscript>4</Subscript> compound

The SnTe–Sb₂Te₃–Te system has been studied in the temperature range 300–430 K using emf measurements on reversible concentration cells of the type (–)SnTe(s) | liquid electrolyte, Sn²⁺ |(Sn–Sb–Te)(s)(+). The system has been shown to consist of two three-phase regions, separated by the SnSb₂Te₄–Te tie line. The best fit equation for the temperature-dependent emf data has been used to evaluate the partial thermodynamic functions of the SnTe and Sn in the alloys. Using these data, subsolidus phase diagram data for the SnTe–Sb₂Te₃–Te system, and relevant thermodynamic functions for SnTe and Sb₂Te₃, we calculated the standard Gibbs energy of formation, standard enthalpy of formation, and standard entropy of the SnSb₂Te₄ compound.     

Homogeneity ranges of Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>Cl and Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>Br

This paper systematizes phase-diagram data for the Tl-TlCl(Br)-Te systems and presents their 500-K subsolidus phase diagrams. Tl₅Te₂Cl and Tl₅Te₂Br (Tl₅Te₃ structure) are shown to be nonstoichiometric compounds with wide homogeneity ranges, which have been accurately determined using emf measurements, x-ray diffraction, and microhardness tests. Using emf data for reversible concentration cells with a thallium electrode, we have evaluated the partial thermodynamic functions of the thallium in the alloys studied, the standard thermodynamic functions of formation of Tl₅Te₂Cl and Tl₅Te₂Br, and their standard entropies. The crystal chemistry of these phases of variable composition is discussed in relation to the Tl₅Te₃ structure.     

Thermodynamic properties of Tl5Se2Cl-based solid solutions

The equilibrium subsolidus phase diagram of the TlCl-Tl₂Se-TlSe system has been mapped out using X-ray diffraction analysis and emf measurements on thallium concentration cells. The Tl₅Se₂Cl compound has been shown to be a nonstoichiometric phase with a homogeneity region extending over a considerable part of the Tl₂Se-Tl₅Se₂Cl-Tl₅Se₃ composition triangle. The emf results have been used to evaluate the relative partial thermodynamic functions of the thallium in the alloys studied and the standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰(298 K), and S ⁰(298 K)) of Tl₅Se₂Cl and Tl₅Se₂Cl-based solid solutions.     

Thermodynamic properties and homogeneity regions of Tl<Subscript>6</Subscript>SCl<Subscript>4</Subscript> and Tl<Subscript>5</Subscript>Se<Subscript>2</Subscript>Cl

In this activity system Tl-Tl₂X-X (X = S, Se)are studied using emf measurements of concentration chains relative thallic electrode. The solid phase diagrams of these systems are clarified, homogeneity areas of the compounds Tl₆SCl₄ and Tl₅Se₂Cl are determined. On the basis of emf measurement results, relative partial molar functions of thallium in alloys and standard integral thermodynamic functions (ΔG ⁰(298 K), ΔH ⁰ (298 K), ΔS ⁰ (298 K)) of the ternary compounds Tl₆SCl₄ and Tl₅Se₂ Cl and phases of variable composition based on the latter are calculated.     

System Cu-Rh-O: Phase diagram and thermodynamic properties of ternary oxides CuRhO2 and CuRh2O4

An isothermal section of the phase diagram for the system Cu-Rh-O at 1273 K has been established by equilibration of samples representing eighteen different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). In addition to the binary oxides Cu₂O, CuO, and Rh₂O₃, two ternary oxides CuRhO₂ and CuRh₂O₄ were identified. Both the ternary oxides were in equilibrium with metallic Rh. There was no evidence of the oxide Cu₂Rh₂O₅ reported in the literature. Solid alloys were found to be in equilibrium with Cu₂O. Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. Yttria-stabilized zirconia was used as the solid electrolyte, and an equimolar mixture of Rh+Rh₂O₃ as the reference electrode. The reference electrode was selected to generate a small electromotive force (emf), and thus minimize polarization of the three-phase electrode. When the driving force for oxygen transport through the solid electrolyte is small, electrochemical flux of oxygen from the high oxygen potential electrode to the low potential electrode is negligible. The measurements were conducted in the temperature range from 900 to 1300 K. The thermodynamic data can be represented by the following equations: {fx741-1} where Δ_f(ox) G ^o is the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides. Based on the thermodynamic information, chemical potential diagrams for the system Cu-Rh-O were developed.     

Standard thermodynamic properties of Ag3Sb and Ag6Sb evaluated by EMF measurements

The standard thermodynamic properties of the intermetallic compounds Ag₃Sb and Ag₆Sb (the minerals dyscrasite and allargentum, respectively) in the Ag-Sb system have been determined in the temperature range 350–500 K at atmospheric pressure using a solid-state galvanic cell (emf method). The results have been used to propose recommended standard thermodynamic functions of formation at 298.15 K and 10₅ Pa. The Gibbs energy, entropy, and enthalpy of Ag₃Sb(cr) are ?5934 ± 1277 J/mol, 195.89 ± 2.54 J/(mol K), and 841 ± 1046 J/mol, respectively, and those of Ag₆Sb(cr) are ?6637 ± 3064 J/mol, 332.40 ± 5.99 J/(mol K), and 2778 ± 2491 J/mol, respectively.     

Oxygen potentials,Gibbs' energies and phase relations in the Cu-Cr-O system

Thermodynamic properties of ternary compounds, cuprous and cupric chromites (CuCro₂, CuCr₂O₄), and oxygen potentials corresponding to three three-phase regions in the Cu-Cr-O system have been measured in the temperature range 900 to 1350 K using a solid state galvanic cell incorporating calcia-stabilized zirconia. Cuprous chromite was found to be nearly stoichiometric. The compositions of non-stoichiometric cupric chromite saturated with CuO and Cr₂O₃ have been determined using electron microprobe and energy dispersive X-ray analysis. The results of this study resolve discrepancies in Gibbs' energies of cuprous and cupric chromites reported in the literature. A ternary phase diagram for the Cu-Cr-O system at 1150 K and phase relations in air for the Cu₂O-CuO-Cr₂O₃ system as a function of temperature have been derived based on the new thermodynamic data. The phase diagram given in the literature is found to be inaccurate.     

Phase equilibria and properties of solid solutions in the Tl<Subscript>5</Subscript>Te<Subscript>3</Subscript>-Tl<Subscript>9</Subscript>BiTe<Subscript>6</Subscript>-Tl<Subscript>5</Subscript>Te<Subscript>2</Subscript>I system

Phase equilibria in the Tl₅Te₃-Tl₉BiTe₆-Tl₅Te₂I system, containing ternary structural analogs of Tl₅Te₃, have been studied by differential thermal analysis, X-ray diffraction, microhardness tests, and emf measurements using concentration cells with a thallium electrode. A number of T-x sections, the 760- and 800-K sections, and the liquidus and solidus projections of the phase diagram are constructed, and the composition dependences of lattice parameters, microhardness, and emf are obtained. The results demonstrate that, despite the presence of a liquid-liquid miscibility gap, the system contains a continuous series of solid solutions isostructural with Tl₅Te₃.     

Synthesis and properties of a copper(I) cobalt(II) double sulfite

The Pourbaix diagrams of the Cu–H₂SO₄–H₂O and Co–H₂SO₄–H₂O systems have been refined and the stability regions of sulfite phases in the diagrams have been identified. Phase diagrams of copper(I) copper( II) and copper(I) cobalt(II) double sulfites have been mapped out. The double sulfites Cu₂SO₃ · СuSO₃ and Cu₂SO₃ · СoSO₃ have been isolated from an aqueous solution saturated with sulfur dioxide. We have obtained electron paramagnetic resonance spectra of the double sulfite Cu₂SO₃ · СoSO₃ and characterized it by X-ray diffraction, IR spectroscopy, particle size analysis, and thermogravimetry. A foundation has been laid for the thermodynamic prediction of the synthesis of the Cu₂SO₃ · MSO₃ (M = Cu, Co) double sulfites.     

The Tl–I phase diagram revisited and the thermodynamic properties of thallium iodides

The Tl–I system has been studied using differential thermal analysis, X-ray diffraction, and emf measurements on TlI concentration cells. A more accurate Tl–I phase diagram is presented, according to which the compounds existing in the Tl–I system are TlI, Tl₂I₃, and TlI₃. Thallium monoiodide melts congruently at 715 K and undergoes a polymorphic transformation at 440 K. The other iodides melt peritectically at 535 and 404 K, respectively. In contrast to what was reported previously, no compound of composition Tl₃I₄ has been obtained. Using experimental emf data, we evaluated relative partial molar thermodynamic functions of the TlI in alloys of the TlI–I system and the standard Gibbs free energy, enthalpy of formation, and standard entropies of TlI₃ (?ΔG ₂₉₈ ⁰ = 142.79 ± 0.73 kJ/mol, ?ΔH ₂₉₈ ⁰ = 135.37 ± 2.85 kJ/mol, and S ₂₉₈ ⁰ = 263.3 ± 7.4 J/(mol K)) and Tl₂I₃ (271.39 ± 1.47, 262.40 ± 5.34, and 322.8 ± 13.2).     

Vibrational studies of copper thiogallate solid solutions

Vibrational spectra of Ga₂S₃–Cu₂S solid solutions have been studied at room temperature. Raman scattering and far-infrared spectra of the zinc-blende structure were carried out in the compositional range 0.10≤n≤0.25. All the spectra can be interpreted using a localized model considering the decoupled, weakly deformed GaS₄ tetrahedral units. The presence of copper atoms in the structure is detected by a hardening of the Ga–S bonds and a modification of the tetrahedral network. Vibrational modes of the three crystalline forms of the semiconducting ternary compound CuGaS₂ have also been investigated. The results show that the mode frequencies are very sensitive to a small variation in the compound stoichiometry.