E. G. Osadchii

The system Ag-Au-Se: Phase relations below 405 K and determination of standard thermodynamic properties of selenides by solid-state galvanic cell technique

Abstract The existence of the only ternary compound, Ag3AuSe2 (fischesserite), in the Ag-Au-Se system was confirmed by solid-state annealing method. The selenium analog of petrovskaite (AgAuS) was not observed under the experimental conditions (in the temperature range of 350-773 K and own vapor pressure). The solid-state reactions 2Ag(cr) + Se(s) = Ag2Se(cr) Ag(cr) + Ag3AuSe2(cr) = 2Ag2Se(cr) + Au(cr) 3Ag(cr) + 2AuSe(s) = Ag3AuSe2(cr) + Au(cr) were studied by the electromotive force (EMF) technique in all solid-state galvanic cells with Ag4RbI5 as a solid electrolyte. The experiments were run in a dry argon gas flow at atmospheric pressure. The following standard thermodynamic properties of the stable phases were determined at 298.15 K and 1 bar (105 Pa): ΔfG°(Ag2Se, low naumannite) = -49470 (±130) J/mol, S°(Ag2Se, low naumannite) = 149.99 (±0.56) J/(K·mol); ΔfG°(Ag2Se, high naumannite) = -47430 (±290) J/mol, S°(Ag2Se, high naumannite) = 169.01 (±0.78) J/(K·mol); ΔfG°(Ag3AuSe2, fischesserite) = -86450 (±320) J/mol, S°(Ag3AuSe2, fischesserite) = 290.80 (±1.26) J/(K·mol); ΔfG°(β-AuSe) = -4110 (±1300) J/mol; S°(β-AuSe) = 75.49 (±3.55) J/(K·mol). The phase transition point for low naumannite-high naumannite was determined at Ttrs = 405.4 K, with the enthalpy of transition of ΔtrsH = -7713 (±550) J/mol.

Determination of standard thermodynamic properties of sulfides in the Ag-Au-S system by means of a solid-state galvanic cell

Abstract Thermodynamic properties of the following phase reactions in the Ag-Au-S system have been investigated via electromotive force (EMF) measurements in solid-state galvanic cells with Ag4RbI5 as a solid electrolyte: Ag(cr) + Ag3AuS2(cr) = 2Ag2S(cr) + Au(cr) Ag(cr) + 2AgAuS(cr) = Ag3AuS2(cr) + Au(cr) Ag(cr) + Au2S(cr) = AgAuS(cr) + Au(cr) AgAuS(cr) + Ag2S(cr) = Ag3AuS2(cr) The EMF temperature dependences observed for these reactions, together with auxiliary thermodynamic properties for Ag2+S, acanthite, from Robie and Hemingway (1995), result in the following standard thermodynamic properties at 298.15 K and 1 bar (105 Pa): ΔfGo(Ag3AuS2, cr) = -69478(200) J/mol and So(Ag3AuS2, cr) = 273.37(56) J/(mol·K) (uytenbogaardtite), ΔfGo(AgAuS, cr) = -27621(210) J/mol and So(AgAuS, cr) = 128.11(60) J/(mol·K) (petrovskaite), and ΔfGo(Au2S, cr) = 1077(650) J/mol and So(Au2S, cr) = 128.1(2.0) J/(mol·K). Au2S(cr) is a thermodynamically metastable phase, but the values of its thermodynamic functions are open to discussion

Single crystal growth and characterization of tetragonal FeSe1−x superconductors

The plate-like single crystals of tetragonal (P4/nmm) FeSe1−x superconductors were grown using the KCl–AlCl3 flux technique which produced single crystalline tetragonal samples of about 4 × 4 × 0.1 mm3 dimensions. The energy dispersive X-ray spectroscopy established a ratio of Fe : Se = 1 : 0.96 ± 0.02. The resistivity and magnetization measurements revealed a sharp superconducting transition at Tc = 9.4 K. Multiple Andreev reflections spectroscopy pointed to the existence of two-gap superconductivity with the gap values ΔL = 2.4 ± 0.2 meV and ΔS = 0.75 ± 0.1 meV at 4.2 K.

Determination of thermodynamic properties of silver selenide by the galvanic cell method with solid and liquid electrolytes

The data on the standard thermodynamic functions of silver selenide (naumannite) determined by the EMF method with the electrolyte representing either silver chloride or a glycerol solution of KCl with AgCl are shown. The procedure of measurements with the mentioned electrolytes is developed.

Synthesis of Chalcogenide and Pnictide Crystals in Salt Melts Using a Steady-State Temperature Gradient

Some examples of growing crystals of metals, alloys, chalcogenides, and pnictides in melts of halides of alkali metals and aluminum at a steady-state temperature gradient are described. Transport media are chosen to be salt melts of eutectic composition with the participation of LiCl, NaCl, KCl, RbCl, CsCl, AlCl3, AlBr3, KBr, and KI in a temperature range of 850–150°C. Some crystals have been synthesized only using a conducting contour. This technique of crystal growth is similar to the electrochemical method. In some cases, to exclude mutual influence, some elements have been isolated and forced to migrate to the crystal growth region through independent channels. As a result, crystals of desired quality have been obtained using no special equipment and with sizes sufficient for study under laboratory conditions.

Potentiometric study of the stability of Eu3+ acetate complexes as a function of pressure (1–1000 bar) at 25°C

The stability of europium acetate complexes was examined potentiometrically at 25°C as a function of pressure in the range of 1–1000 bar. The measurements were carried out in an isothermal potentiometric cell with a liquid junction. The cell consisted of a pH glass electrode and an Ag, AgCl (3m KCl) reference electrode. The calibration of the cell on standard solutions has demonstrated that its electromotive force is independent of pressure. Based on pH measurements under various pressures in four acetate solutions with pH from 3 to 4.7 and containing 0.0142m Eu, we determined the standard partial mole volumes and the HKF parameters for the complexes Eu(Ac)2+ and Eu(Ac)2+. The baric dependence of the ΔfG0 of the third complex, Eu(Ac)30, was evaluated from correlations. The stability of all three Eu acetate complexes decreased with pressure: as the pressure was increased from 1 to 1000 bar, the constants of formation of the complexes decreased by factors of 1.5–3 at 25°C and 2–6 at 170°C.

Thermodynamic study of monoclinic pyrrhotite in equilibrium with pyrite in the Ag-Fe-S system by solid-state electrochemical cell technique

Abstract An equilibrium mixture of monoclinic pyrrhotite and pyrite was synthesized in the eutectic AlCl3- KCl melt at 525 K. The reaction 7FeS2(cr) + 12Ag(cr) = 8Fe0.875S(cr) + 6Ag2S(cr) was studied by an electromotive force technique in an all-solid-state electrochemical cell with an Ag+-conductive solid electrolyte in Ar at atmospheric pressure: (-) Pt | Ag | AgI | Ag2S, Fe0.875S, FeS2 | Pt (+). In the 490-565 K temperature range a linear electromotive force vs. temperature trend was obtained from which the temperature dependence of the sulfur fugacity was determined for the monoclinic pyrrhotitepyrite equilibrium: logfS2(mpo+py) = 14.079 - 14406⋅T-1, (500 < T/K < 565). In addition, standard thermodynamic functions were calculated for monoclinic pyrrhotite Fe0.875S at 298 K and atmospheric pressure: ΔGf(mpo, 298.15 K) = -(136 200 ± 3000) J/mol, S°(mpo, 298.15 K) = (66.7 ± 1.3) J/(mol-K), ΔHf(mpo, 298.15 K) = -(157 400 ± 3000) J/mol. Gaseous sulfur, S2-ideal gas at 1 bar (105 Pa) pressure- was taken as a standard state for sulfur.

Standard thermodynamic properties of Pd and Pt ditellurides

Platinumgroup elements (PGE) are transition metals of group VIII in the periodic table of chemical elements. Although similarities between PGE are emphasized in geochemistry, the types of their interac� tions with other elements and the specifics of their electron structure make it possible to classify PGE into three groups. Groups 1 and 2 include Ru with Os and Ir with Rh, respectively, and group 3 consists of Pt and Pd, which are the most chemically active PGE (this applies, first of all, to Pd) because of the structure of their electron shells. The most widely spread natu� rally occurring PGE tellurides are those of Pt and Pd, which usually contain Bi, and no pure binary com� pounds have ever been found. Pd and Pt ditellurides are typically contained in ores at Cu-Ni mineral deposits. An important problem is revealing the factors responsible for the different behavior of Pt and Pd in mineralforming processes, an issue that cannot be elucidated without knowing properties of the most widely spread minerals at these deposits. Our research was focused on the calorimetric determination of the enthalpy of formation of Pt and Pd ditellurides, with the use of literature data on lowtemperature adiabatic calorimetry and electrochemical measurements. Pt and Pd ditellurides can be easily synthesized by heating corresponding stoichiometric mixtures in ampoules of quartz glass evacuated to

Application of solid electrolytes α-AgI and RbAg4I5 for refining phase diagrams and determining standard thermodynamic functions of compounds in silver-containing systems

Standard thermodynamic properties of minerals and phases of ternary systems Ag-Au-X (X = S, Se, Te) are determined by measuring the EMF in the cells with a common gas space and Ag4RbI5 as the solid electrolyte. By this means, thermodynamic functions of the following minerals and phases are determined: Au2S, Ag3AuS2 (uytenbogaardtite), AgAuS (petrovskaite), Ag2Se (naumannite), AuSe, Ag3AuSe2 (fischesserite), and Ag5Te3 (stuetzite). Thermodynamics of a pyrite-pyrrhotite equilibrium in the Ag-Fe-S system is studied in a cell with a solid electrolyte based on silver iodide at 500–730 K and atmospheric pressure.

Determination of thermodynamic properties of triple phases formed in different regions of phase diagram of the Ag-Bi-S system using EMF measurements

The technique of measurement of electromotive force (EMF technique) in reversible cells of solid-state galvanic cells with RbAg4I5 as solid electrolyte was used to determine standard thermodynamic properties of triple phases in the system of Ag-Bi-S in equilibrium with metallic bismuth. The results are compared to the available literature data obtained in equilibrium with crystalline sulfur.