Cu<Subscript>4</Subscript>RbCl<Subscript>3</Subscript>I<Subscript>2</Subscript> solid superionic conductor in thermodynamic study of three-component copper chalcogenides

The Cu-B-Se (B = In, As, Sb, Bi) systems are studied by measurement of EMF for concentration circuits vs. a copper electrode in the temperature range of 300–430 K. A solid superionic Cu₄RbCl₃I₂ conductor is used as an electrolyte. Diagrams of solid-phase equilibriums in the studied systems are constructed. Partial molar functions of alloyed copper are calculated on the basis of the equations of the temperature dependences of EMF. Potential-forming reactions corresponding to the measured EMF values are determined on the basis of the phase diagrams and standard thermodynamic formation functions and standard entropies of ternary compounds are calculated.     

Thermodynamic study of glasses in Ag-As-Se system using EMF method with Ag<Subscript>4</Subscript>RbI<Subscript>5</Subscript> solid electrolyte

The EMF method with Ag₄RbI₅ solid electrolyte was used to study silver solubility in Ag-As-Se glasses on the basis of the cross-sections of (I) Ag-As_0.25Se_0.75, (II) Ag-As_0.33Se_0.67, (III) Ag-As_0.4Se_0.6, and (IV) Ag-As_0.5Se_0.5. It is found that silver solubility reaches 30 and 40 at % in sections (I), (IV) and (II), (III), accordingly. The data of EMF measurements were used as a basis for calculation of partial polar functions of Ag in glasses. The Gibbs-Duhem equations were integrated to calculate thermodynamic functions of silver dissolution in vitreous As _x Se_{1 − x} (x = 0.25; 0.33; 0.4; 0.5), from which the corresponding data for the latter were used to obtain the standard integral thermodynamic functions of the mixing of glasses. The obtained results were compared with the thermodynamic data for crystalline silver selenoarsenites.     

Thermodynamic Properties of AgIn<Subscript>2</Subscript>Te<Subscript>3</Subscript>I and AgIn<Subscript>2</Subscript>Te<Subscript>3</Subscript>Br,Determined by EMF Method

Differential thermal analysis (DTA), X-ray diffraction (XRD), and electromotive force (EMF) are used to triangulate Ag–In–Te–I(Br) systems in the vicinity of compounds AgIn₂Te₃I and AgIn₂Te₃Br. The three-dimensional position of the AgIn₂Te₃I–InTe–Ag₂Te–AgI and AgIn₂Te₃Br–InTe–Ag₃TeBr phase areas with respect to the figurative points of silver is used to create equations of potential-determining chemical reactions. The potential-determining reactions are conducted in (?)C|Ag|Ag₃GeS₃I(Br) glass|D|C(+) electrochemical cells (ECCs), where C stands for inert (graphite) electrodes, Ag and D are ECC electrodes (D denotes alloys of one-, three-, and four-phase areas), and Ag₃GeS₃I and Ag₃GeS₃Br glasses are membranes with purely ionic Ag⁺ conductivity. Linear parts of the temperature dependences of the cell EMFs are used to calculate the standard integral thermodynamic functions of saturated solid solutions based on AgIn₂Te₃I and AgIn₂Te₃Br, and the relative partial thermodynamic functions of silver in the stoichiometric quaternary compounds.     

Phase relations in the Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>-Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> system from room temperature to melting

Phase relations in the Zn₂V₂O₇-Cu₂V₂O₇ system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents of the system are solid solutions based on Zn₂V₂O₇ and Cu₂V₂O₇ polymorphs and their coexistence regions. The generation of α-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu_{2 − 2x} Zn_2x V₂O₇ homogeneity range is 5 mol % Zn₂V₂O₇. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu₂V₂O₇ and β-Cu₂V₂O₇ base solid solutions. At still higher temperatures, β-Zn_{2 − 2x} Cu_2x V₂O₇ and α-Cu_{2 − 2x} Zn_2x V₂O₇ coexist in the mixed-phase region. β-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu₂V₂O₇-base solid solution is 9 to 65 mol % Zn₂V₂O₇ at 615 ± 5°C, expanding to 0 mol % Zn₂V₂O₇ with rising temperature. Original Russian Text ￠ T.I. Krasnenko, M.V. Rotermel’, S.A. Petrova, R.G. Zakharov, O.V. Sivtsova, A.N. Chvanova, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1755–1762.     

Phase equilibria in the PbSe-Bi<Subscript>2</Subscript>Se<Subscript>3</Subscript>-Se system and thermodynamic properties of intermediate phases

The Pb-Bi-Se system in the PbSe-Bi₂Se₃-Se-Se composition region was studied by measurement of concentration circuits of the type (−) PbSe(solid) liquid electrolyte, Pb²⁺(Pb-Bi-Se)(solid) (+) in the temperature range 300–430 K and by X-ray powder diffraction. A solid-phase equilibrium diagram was constructed, and the formation was confirmed for the ternary compounds Pb₅Bi₆Se₁₄, Pb₅Bi₁₂Se₂₃, and Pb₅Bi₁₈Se₃₂, which belong to the homologous series [(PbSe)₅] _m · [(Bi₂Se₃)₃] _n . From the emf versus temperature equations, the partial thermodynamic functions [`(DG)]\overline {\Delta G}, [`(DH)]\overline {\Delta H}, [`(DS)]\overline {\Delta S} of PbSe in alloys were calculated. Based on the solid-phase equilibrium diagram from these partial molar quantities using the corresponding data for PbSe and Bi₂Se₃, the standard thermodynamic functions of formation and standard entropies of the above ternary compounds were calculated.     

Tysonite-type solid solutions in the BiF<Subscript>3</Subscript>-BiOF-BaF<Subscript>2</Subscript> system: Polymorphism and anionic conductivity

Tysonite solid solutions Bi_1−x Ba _x O _y F_3−x−2y in the BiF₃-BiOF-BaF₂ system were obtained by solid-phase synthesis in sealed copper tubes in an argon atmosphere at 873 K with subsequent quenching. The solid solutions were studied by X-ray diffraction, electron diffraction, and impedance spectroscopy. On the basis of X-ray powder diffraction data, the homogeneity ranges of the tysonite solid solutions were determined and the scheme of their location in the BiF₃-BiOF-BaF₂ system at 873 K was suggested. Aliovalent substitutions in both the cation and anion sublattices Ba²⁺ → Bi³⁺ and O²⁻ → F⁻ made it possible to vary the concentration of anion vacancies. It was found that, at a high concentration of anion defects at 873 K, the hexagonal tysonite modification with space group P6₃/mmc is stable. With a decrease in the defect concentration, the trigonal tysonite modification with space group $ P\bar 3c1 $ P\bar 3c1 becomes stable. An ordered monoclinic tysonite-type modification BiO _y F_{3 − 2y} (0.13 < y < 0.23) was revealed. For the homogeneity ranges of all tysonite phases, dependences of the unit cell parameters and conductivity on the composition along the sections with a constant barium or oxygen content were reported. The most probable location of oxygen anions and anion vacancies in the tysonite structure is discussed.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

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.     

Thermodynamics of Zr<Subscript>52.5</Subscript>Cu<Subscript>17.9</Subscript>Ni<Subscript>14.6</Subscript>Al<Subscript>10</Subscript>Ti<Subscript>5</Subscript> bulk metallic glass forming alloy

Recently, multicomponent glass forming alloys have been found which exhibit extraordinary glass forming ability and cooling rates of less than 100 K/s are sufficient to suppress nucleation of crystalline phases and consequently bulk metallic glass (BMG) is formed. The undercooled melts of BMG systems have high thermal stability in the undercooled region. Therefore, it is interesting to study the thermodynamics of such materials. This article investigates the thermodynamic behavior of a BMG system namely Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ by estimating the Gibbs free energy difference ΔG, entropy difference ΔS, enthalpy difference ΔH between the undercooled liquid and corresponding equilibrium crystalline solid phase, in the entire temperature range from T _m to T _K. Glass forming ability (GFA) of this system has been investigated through various GFA parameters indicating the degree of ease of glass formation.     

Phase formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

Solid-phase interactions in the V₂O₅-Ta₂O₅-MoO₃ system were studied. The formation of com- pounds TaVO₅ and VTa₉O₂₅ in the V₂O₅-Ta₂O₅ binary system was verified. Tetragonal VTa₉O₂₅-base solid solutions of the general formula Ta_{5 + 4x} V_{5 − 4x} O₂₅ (x = 0.25–1) and TaVO₅-base solid solutions of the general formula Ta _x Mo_{1 − x} V_{2 − x} O_{8 − 3x} (x = 0.625–1) were found to form. Subsolidus phase equilibria in the V₂O₅-Ta₂O₅-MoO₃ were determined.     

A thermodynamic study of Cu—Tl—S system by EMF method with Cu4RbCl3I2 solid electrolyte

The Cu—Tl—S system was studied by the EMF method with Cu₄RbCl₃I₂ solid Cu⁺-conducting electrolyte within the temperature range from 300 to 390 K. The earlier plotted solid-phase equilibrium diagram of this system was confirmed, the partial copper molar functions $ (\Delta \bar G,\Delta \bar H,\Delta \bar S) $ ) in alloys and standard thermodynamic formation functions and standard entropies of CuTlS₂, CuTlS, Cu₃TlS₂, and Cu₉TlS₅ ternary compounds were calculated. The derived results demonstrated an opportunity of thermodynamic studies of copper-containing ternary systems of this modification by EMF method even if they contain a less noble component than copper.     

Synthesis and characterization of ambient temperature superionic solids in the composite system CuI–Ag<Subscript>2</Subscript>O–TeO<Subscript>2</Subscript>

The present work deals with the composite system (CuI) _x –(Ag₂O–TeO₂)_{100– x} , where x=30, 35, 40, 45, 50, 55, 60, 65, 70 and 75 mol%, respectively, synthesized by a solid-state reaction route. Powder specimens were analysed using differential scanning calorimetry, X-ray diffraction and Fourier transform infrared techniques. These studies have revealed the formation of Cu₃TeO₆, AgI and/or other phases. The ambient temperature electrical conductivities obtained for the samples using a complex impedance method were found to lie in the range 10^–6–10^–4 Scm^–1, with low activation energies, thus indicating their superionic nature. The typical composition 35CuI–32.5Ag₂O–32.5TeO₂ was identified as the best conducting one, having an electrical conductivity of 6×10^–4 Scm^–1 at 296 K and an activation energy of 0.23 eV. Ion transport number measurements carried out using Wagner's polarization technique as well as by an electromotive force method suggested that silver ions were responsible for the observed transport features of the composite system. Electronic Publication     

Synthesis of nonequilibrium Ir<Subscript>x</Subscript>Re<Subscript>1-x</Subscript> solid solutions. Crystal structure of [Ir(NH<Subscript>3</Subscript>)<Subscript>5</Subscript>Cl]<Subscript>2</Subscript>[ReCl<Subscript>6</Subscript>]Cl<Subscript>2</Subscript>

Synthesis of five binary complex salts with an [Ir(NH₃)₅Cl]²⁺ complex cation is described. The counterions are [ReCl₆]^2–, [IrCl₆]^2–, [ReBr₆]^2–, and Cl^–. A polycrystal X-ray diffraction study has been performed for [Ir(NH₃)₅Cl]₂[ReCl₆]Cl₂, and its crystal structure has been determined. A series of Ir _x Re_1–x phases (0.5 x > 1) were obtained by reductive thermolysis. For the Ir-Re system, the history of the V/Z(x) dependence has been refined.Original Russian Text Copyright © 2004 by S. A. Gromilov, S. V. Korenev, I. V. Korolkov, K. V. Yusenko, and I. A. BaidinaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 508–515, May–June 2004.     

New phase in the system FeVO<Subscript>4</Subscript>-Cd<Subscript>4</Subscript>V<Subscript>2</Subscript>O<Subscript>9</Subscript>

A new phase Cd₄Fe_7+xV_9+xO_37+4x, where −0.5<x<1.5, has been obtained in the solid-state in the FeVO₄−Cd₄V₂O₉ system. The temperature of incongruent melting and the unit cell volume of this phase decrease with decreasing the content of cadmium. The IR spectrum and SEM image of the new phase are presented.     

Glass transition and crystallization study of chalcogenide Se<Subscript>70</Subscript>Te<Subscript>15</Subscript>In<Subscript>15</Subscript> glass

Differential scanning calorimetry data at different heating rates (5, 10, 15 and 20 °C min⁻¹) of Se₇₀Te₁₅In₁₅ chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se₇₀Te₁₅In₁₅ alloy has three-dimensional growth. The average values of the activation energy for glass transition, E _g, and crystallization process, E _c, are (154.16 ± 4.1) kJ mol⁻¹ and (98.81 ± 18.1) kJ mol⁻¹, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T _rg), Hruby’ parameter (K _gl) and fragility index (F _i) indicate that the prepared glass is obtained from a strong glass forming liquid.     

Second Dissociation Constant of H<Subscript>2</Subscript>Te and the Absorption Spectra of HTe<Superscript>–</Superscript>, Te<Superscript>2–</Superscript> and Te<Subscript>2</Subscript><Superscript>2–</Superscript> in Aqueous Solution

We have measured the second acid dissociation constant, K _2a , at several ionic strengths for hydrogen telluride (H₂Te) using the Charge Transfer to Solvent (CTTS) uv spectra of its anions HTe⁻ and Te²⁻. Since it is produced in our solutions, we have also determined the spectra of Te₂ ²⁻ both in the uv and in the visible regions. At 25 ^∘C, K _2a = (1.28 ± 0.02) × 10⁻¹² by extrapolation to zero ionic strength. Its value at an ionic strength equal to 0.5 mol.dm^-3 was estimated to be (8.7 ± 0.2) × 10⁻¹². The solution thermodynamics of these species are also discussed and comparisons are made to related acids.     

Phase equilibria and isomorphism in the LiVWO<Subscript>6</Subscript>-NaVWO<Subscript>6</Subscript> system

Compounds of composition Li _x Na_{1 − x} VWO₆ (0 ≤ x ≤ 1), which are synthetic analogues of brannerite-type minerals, were produced for the first time by solid-state synthesis at high temperatures. The structure of the compounds and their unlimited miscibility in the solid phase in the LiVWO₆-NaVWO₆ binary system were determined by X-ray diffraction. The phase equilibrium diagram was studied by differential thermal analysis together with thermodynamic modeling. It was found that the system under investigation is described by the regular solid solutions model.     

The heat capacity of solid antimony telluride Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>

The literature data on the heat capacity of solid antimony telluride over the range 53–895 K were analyzed. The heat capacity of Sb₂Te₃ was measured over the range 350–700 K on a DSM-2M calorimeter. The equation for the temperature dependence was suggested. The thermodynamic functions of Sb₂Te₃ were calculated over the range 298.15–700 K.     

Thermal Decomposition of Ti<Subscript>5</Subscript>(Se,Te)<Subscript>8</Subscript> in Argon and Nitrogen Atmospheres

Chalcogenides TiSe_1.60−x Te_x (0 ≤ x ≤ 1.60), forming a continuous series of hexagonal solid solutions, were prepared by the direct ampule procedure. The thermal decomposition of TiSe_1.60−x Te_x was studied for the samples with x = 0, 0.16, 0.80, 1.44, and 1.60 in Ar and N₂ atmospheres in the course of heating from 25 to 1000°C. The selenide undergoes no weight loss under Ar, in contrast to the telluride which disproportionates and loses weight owing to the formation of volatile TiTe₂. At high temperatures, tellurides are more sensitive than selenides to the presence of nitrogen: The disproportionation is accompanied by the reaction of TiTe₂ with N₂, yielding low-volatile titanium nitride and free tellurium. Titanium selenide and telluride as components of the solid solutions behave similarly to the corresponding individual chalcogenides.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1063–1067.Original Russian Text Copyright © 2005 by Pankratova, Zvinchuk, Suvorov, Hatanpaa, Kozlov, Leskela.