Ion Transfer in CdF<Subscript>2</Subscript>-based Iso- and Polyvalent Solid Solutions

The ionic conductivity of solid solution Cd_0.77Sr_0.23F₂ is 1.6 × 10⁻⁴ S/cm at 500 K. The conduction mechanism changes from a vacancy mechanism to an interstitial one at 523–553 K. In solid solutions Cd_0.9R_0.1F_2.1 (R = La-Lu, Y), the activation enthalpy of conduction decreases from 0.9 to 0.8 eV with decreasing ionic radius of R³⁺, raising the 500-K conductivity from 6 ×10⁻⁶ S/cm for La³⁺to 6 × 10⁻⁵ S/cm for Lu³⁺. For crystalline Cd_0.95In_0.05F_2.05, ionic and electronic conductivities at 313 K equal 5 × 10⁻⁴ and 5 − 10⁻⁶ S/cm.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 627–632.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Sul’yanova, Sobolev.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Heat capacity, enthalpy and entropy of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7

The heat capacity and the enthalpy increments of strontium niobate Sr₂Nb₂O₇ and calcium niobate Ca₂Nb₂O₇ were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (720–1370 K). Temperature dependencies of the molar heat capacity in the form C_pm = 248.0 + 0.04350T − 3.948 × 10⁶/T² J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and C_pm = 257.2 + 0.03621T − 4.434 × 10⁶/T² J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇ were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, S_m°(298.15 K) = 238.5 ± 1.3 J K⁻¹ mol⁻¹ for Sr₂Nb₂O₇ and S_m°(298.15 K) = 212.4 ± 1.2 J K⁻¹ mol⁻¹ for Ca₂Nb₂O₇, were evaluated from the low-temperature heat capacity measurements.     

Molecular dynamics study of phase transition and nucleation in supercooled clusters of potassium iodide

In a series of molecular dynamics (MD) runs on (KI)₁₀₈ clusters, the Born–Mayer–Huggins potential function is employed to study structural, energetic, and kinetic aspects of phase change and the homogeneous nucleation of KI clusters. Melting and freezing are reproducible when clusters are heated and cooled. The melted clusters are not spherical in shape no matter the starting cluster is cubic or spherical. Quenching a melted (KI)₁₀₈ cluster from 960 K in a bath with temperature range 200–400 K for a time period of 80 ps both nucleation and crystallization are observed. Nucleation rates exceeding 10³⁶ critical nuclei m⁻³ s⁻¹ are determined at 200, 250, 300, 350, and 400 K. Results are interpreted in terms of the classical theory of nucleation of Turnbull and Fisher and of Buckle. Interfacial free energies of the liquid–solid phase derived from the nucleation rates are 7–10 mJ m⁻². This quantity is 0.19 of the heat of transition per unit area from solid to liquid, or about two-thirds of the corresponding ratio which Turnbull proposed for freezing transition. The temperature dependence of σ_sl(T) of (KI)₁₀₈ clusters can be expressed as σ_sl(T)∝T^0.34.     

Quantum-Chemical Investigation of Ionic Association of Lithium Salts LiXF<Subscript>6</Subscript> (X = As,P)

The possibility of formation of various ion clusters for lithium salts LiXF₆ (X = As, P) is studied. The dynamic matrix of the clusters in a gas phase is calculated by numerical and analytical differentiation of the full energy of clusters in the MO LCAO approximation by the Hartree-Fock-Roothaan (HFR) method with the aid of program package PC GAMESS. Stable ionic clusters are ion pairs Li⁺[XF₆]⁻ with bi- and tridentate cation coordination relative to the octahedral anion, ion triplets [XF₆]⁻Li⁺[XF₆]⁻ and Li⁺[XF₆]⁻Li⁺ with bi- and tridentate coordination, and ion dimers { Li⁺[XF₆]⁻}₂ with bidentate coordination. Trimers {Li⁺[XF₆]⁻}₃ and tetramers {Li⁺[XF₆]⁻}₄ in the form of symmetrical ring structures with monodentate coordination are stable only for [AsF₆]⁻. For stable ion species, densities of vibrational states and IR spectra are calculated.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 546–555.Original Russian Text Copyright © 2005 by Popov, Nikiforov, Bushkova, Zhukovskii.     

Electrical Conductance and Volumetric Studies in Aqueous Solutions of DL-Pyroglutamic Acid

Conductivity measurements of DL-pyroglutamic acid and sodium pyroglutamate in dilute aqueous solutions were performed in the 288.15–323.15 K temperature range. The limiting molar conductances of pyroglutamate anion, λ^o(pGlu⁻, T) and the dissociation constants of pyroglutamic acid, K(T) were derived from the Onsager, and the Quint and Viallard conductivity equations. Densities of aqueous solutions with molalities lower than 0.5 mol-kg⁻¹ were determined at 5 K intervals from T = 288.15 K to 333.15 K. Densities served to evaluate the apparent molar volumes, V_2,φ(m, T), the cubic expansion coefficients, α (m,T) and the changes of the isobaric heat capacities with respect to pressure, (∂ C_P/∂ P)_T,m. They were correlated qualitatively with the changes in the structure of water when pyroglumatic acid is dissolved in it.     

Eutectic Composition Systems NaF-DyF3, NaF-HoF3, and MgF2-ScF3 as Ionic Conductors

Electrophysical properties of eutectic composites formed in the NaF-DyF₃, NaF-HoF₃, and MgF₂-ScF₃ systems are studied at 18–528°C. The conductivity of 25NaF-75DyF₃, 25NaF-75HoF₃, and 55MgF₂-45ScF₃ at 20°C (9 × 10⁻⁸, 3 × 10⁻⁷, and 2 × 10⁻⁶ S/cm) exceed that of the initial materials by 2–4 orders of magnitude.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 1010–1013.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Bystrova, Konovalova, Sobolev.     

Regularities of the trans-Influence of Ligand L on the Energy Characteristics of the Metastable Isomers of trans-[RuX4(NO)L]q (L = H2O, NH3, Pyrazine, Cl?, OH?, CN?, NO2?; X = Cl?, NH3)

The geometric structures of the ground state and metastable isomers of the nitroso complexes trans-[RuCl₄(NO)L]^q (L = H₂O, NH₃, pyrazine (Pz), q = −1; Cl⁻, OH⁻, CN⁻, NO ₂ ⁻ , q = −2) and cis[RuCl₄(NO)L]^q (L = Pz, q = −1) were optimized in terms of the density functional theory. The variation of the trans-ligand L influences the relative energy of the metastable isomer with a side NO coordination. The presence of π-acceptor substituents in the trans-ligand L decreases the energy.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 606–611.Original Russian Text Copyright © 2005 by Lyubimova, Sizova.     

Oxygen reduction in acid media at the amorphous Mo–Os–Se carbonyl cluster coated glassy carbon electrodes

An amorphous Mo–Os–Se carbonyl cluster compound has been synthesized in 1,2-dichlorobenzene (b.p.≈180°C) to be tested as an electrocatalyst for molecular oxygen reduction in 0.5 M H₂SO₄. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) performed for the powder supported on pyrolytic carbon show a distribution of nanometer-scale amorphous particles with agglomerations in cluster forms. The catalytic activity was studied by the rotating disc electrode technique. Kinetic studies show a first-order reaction with a Tafel slope of −0.118 V dec⁻¹ and dα/dT=1.55×10⁻³ K⁻¹. In the temperature range 298–343 K, an activation energy of 32 kJ mol⁻¹ was determined.     

Electron spin-lattice relaxation of Cu(II) in Zn(II)-bis(diethyl-diselenocarbamate) single crystals

Using the pulse saturation method the spin-lattice relaxation rate T₁⁻¹ for Cu(II) in Zn(II)-bis(diethyl-diselenocarbamate) was measured in the temperature range 1.5 < T < 33 K. From the T-dependence of T₁⁻¹ the Debye temperature of the host crystal was obtained. The angular dependence of T₁⁻¹ as well as the influence of the hyperfine interaction on T₁⁻¹ are discussed.     

Kinetic Determination of Mercury(II) at Trace Level from Its Catalytic Effect on a Ligand Substitution Process

A catalytic kinetic method (CKM) is presented for the determination of mercury(II) based on its catalytic effect on the rate of substitution of N-methylpyrazinium ion (Mpz⁺) onto hexacyanoferrate(II). The progress of the reaction was monitored spectrophotometrically at 655 nm by registering the increase in absorbance of the product [Fe(CN)₅(Mpz]²⁻ under the reaction conditions: 5 × 10⁻³ mol L⁻¹ [Fe(CN)₆]⁴⁻), 5 × 10⁻⁵ mol L⁻¹ [Mpz⁺], T = 25.0 ± 0.1°C, pH 5.00 ± 0.02 and ionic strength, I = 0.1 mol L⁻¹ (KNO₃). Quantitative rate data at specified experimental conditions showed a linear dependence of the absorbance after fixed time A _t on the concentration of mercury(II) catalyst in the range 20.06–702.1 ng mL⁻¹. The maximum relative standard deviations and percentage errors for the determination of mercury(II) in the range of 20.06–200.6 ng mL⁻¹ were calculated to be 1.7 and 2.7% respectively. The detection limit was found to be 7.2 ng mL⁻¹ of mercury(II). Accuracy (expressed in terms of recoveries) was in the range of 98–103%. Figures of merit and interference due to many cations and anions was investigated and discussed. The applicability of the method was demonstrated by determining the mercury(II) in different synthetic samples and confirming the results using atomic absorption spectrophotometry. The proposed method allowed determination of mercury(II) in the range 20.06–702.1 ng mL⁻¹ with very good selectivity and an output of 30 samples h⁻¹.__________From Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 654–661.Original English Text Copyright © 2005 by Surendra Prasad.This article was submitted by the author in English.     

Kinetic Studies of Bulk Ge22Se78−xBix (x=0, 4 and 8) Semiconducting Glasses

Results of phase transformations, enthalpy released and specific heat of Ge₂₂Se_78–xBi_x(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T _g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T _g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T _g, at a heating rate of 5 K min^–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol^–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T _c–T _g and the enthalpy released during the crystallization process. Below T _g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Superionic Conduction in Complex Fluorides of Antimony(III) MnSbxFy (M—Cations of an Alkali Metal, Ammonium, or Thallium, n = 1–3, and x = 1–4)

Methods of ¹⁹F NMR and impedance spectroscopy are used to investigate the internal mobility of fluoride (ammonium) ions and electrophysical characteristics of complex trivalent antimony fluorides MSb₄F₁₃, MSb₃F₁₀, MSb₂F₇, M₂Sb₃F₁₁, M₃Sb₄F₁₅, and MSbF₄ (M is an alkali cation, ammonium, thallium). The ion motion types in the cationic and anionic sublattices of the fluorides are determined at 150–500 K. The polymorphous transformations in the fluorides are usually phase transitions to a superionic state and their high ionic (superionic) conductivity (σ ≥ 10⁻⁴ to 10⁻² S cm⁻¹ at 400 K) is due to the diffusion motion of ions of fluoride, ammonium, and possibly sodium, potassium, and thallium. The high polarizability of thallium ions favors the development of high mobility of fluoride ions in the fluorides.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 560–572.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Brovkina, Zemnukhova, Sergienko.     

Thermodynamics of Binary and Ternary Copper-, Cadmium,and Indium-Containing Semiconducting Phases: An Electrochemical Study

Optimum compositions of ion-selective membranes in quasi-binary systems CuCl-CdCl₂, LiCl-CdCl₂, and In₂S₃-InCl₃ are selected by a method of coulometric titration in cells with solid electrolytes. Transport numbers for ions are close to unity for the optimum compositions; transport numbers for electrons are vanishingly small ( ≺10⁻³ to 10⁻⁴); the electroconductivity is equal to ≈ 10⁻³ S cm⁻¹ at 200°C; the diffusion coefficients for the current-producing component are on the order of 10⁻⁶ to 10⁻⁷ cm² s⁻¹. When using a solid electrolyte of the composition CuCl-CdCl₂, which contains 30 mol % CdCl₂, methods of emf and electroconduction reveal that the region of homogeneity of copper(I) selenide falls in the region of compositions Cu_1.33Se-Cu_2.67Se.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 721–727.Original Russian Text Copyright © 2005 by Leushina, Kolesnikova, Makhanova, Zlomanov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Influence of coordination on N-H X hydrogen bonds. Part II. Zn(NH3)2Br2 and Ni(NH3)2X2 (X is Cl and Br)

Microcrystalline samples of Zn(NH₃)₂Br₂ and Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻) have been investigated from 100 to 293 K using X-ray diffraction and IR spectroscopy measurements (range 400–4000 cm⁻) performed with isotopically dilute (5% deuterated) samples. Values of Δν(ND)/ΔT for all compounds hint at the existence of hydrogen bonds. Zn(NH₃)₂Br₂ shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molecules takes place in Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻). A comparison between octahedrally coordinated ammoniates [Ni(NH₃)₆]Br₂, Ni(NH₃)₂Br₂ and [Zn(NH₃)₆]Br₂ with tetrahedrally coordinated ones [Zn(NH₃)₂Br₂] leads to the conclusion that the lower coordination number increases the strength of the hydrogen bonds. Because this effect is small, it is not possible to separate the influence of the type of coordinating ions for one coordination number from the influence of the coordination number itself.     

Recombination of HCO and DCO ions with electrons

Recombination of HCO⁺ and DCO⁺ ions with electrons was studied in afterglow plasma. The flowing afterglow with Langmuir probe (FALP) apparatus was used to measure the recombination rate coefficients and their temperature dependencies in the range 150–270 K. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The variations of α_HCO⁺(T) and α_DCO⁺(T) seem to obey the power law: α_HCO⁺(T) = (2.0 ± 0.6) × 10⁻⁷ (T/300)^−1.3 cm³ s⁻¹ and α_DCO⁺(T) = (1.7 ± 0.5) × 10⁻⁷ (T/300)^−1.1 cm³ s⁻¹ over the studied temperature range.     

Etude des propriétés de conduction électrique des polyphosphates: Li3Ba2(PO3)7, LiPb2(PO3)5, LiCs(PO3)2, et αLiK(PO3)2

The electrical conductivity of the crystallized polyphosphates Li₃Ba₂(PO₃)₇, LiPb₂(PO₃)₅, LiCs(PO₃)₂, and αLiK(PO₃)₂ has been determined at different temperatures by impedance spectroscopy. The conductivity, σ, spreads within a range of 1.59 × 10⁻⁸ to 1.79 × 10⁻⁷ S cm⁻¹ at 573 K, and from 1.71 × 10⁻⁵ to 9.86 × 10⁻⁴ S cm⁻¹ at 773 K. The transport should be assumed in the majority by the lithium ions with regard to the structural characteristics of these polyphosphates. The results are discussed and compared to the conductivity properties of other lithium ion conductors.     

Theoretical investigation of the kinetics for the hydrogen abstraction reaction of 1,1,1,2-tetrafluoroethane (HFC-134a) by chlorine radical

The hydrogen abstraction reaction of 1,1,1,2-tetrafluoroethane (HFC-134a) by chlorine radical is investigated by theoretical calculations. Equilibrium geometries and harmonic vibrational frequencies of the reactants, transition state, and products are calculated using high-level ab initio methods. Rate constants of forward and backward reactions for the temperatures from 200 to 1000 K are calculated using classical transition state theory with Eckart tunneling correction, fitted in the expressions k_f (T) = 1.19 × 10⁻²³T^3.93exp (−1110/T), and k_b (T) = 8.86 × 10⁻²⁴T^3.32exp (−959/T) cm³ molecule⁻¹ s⁻¹ for forward and backward reactions, respectively, and are in reasonable agreement with the available experimental values.     

Thermodynamic characteristics of thermal dissociation of platinum trichloride

Single crystals of platinum trichloride were grown for the first time. The IR spectrum of single-crystal PtCl₃ was recorded. The pressure of thermal dissociation of PtCl₃ was measured by the static method with a quartz membrane-gauge zero-pressure manometer. An approximating equation for the dissociation pressure vs. temperature (540 K ≤ T ≤ 775 K) for the reaction 2 PtCl₃(s) → 2 PtCl₂(s) + Cl₂(g) was found. The enthalpy (123.1±1.7 kJ mol⁻¹) and entropy (183.6±2.8 J mol⁻¹ K⁻¹) for the dissociation of PtCl₃(s) were calculated at 298.15 K.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2032–2034, October, 2004.     

Effect of Dibenzo-18-crown-6 on the Polymer Electrolyte/Lithium Anode Interface

Photocured polymer electrolytes, applied onto a porous polypropylene separator, with conduction by lithium cations (1 × 10⁻⁴ S cm⁻¹ at 20°C) are designed. The polymer is formed from a 1 : 1 mixture of oligourethane dimethacrylate and polypropylene glycol monomethacrylate, which are capable of undergoing polymerization via double bonds in a liquid organic electrolyte (0.5 M LiClO₄) in a 1 : 1 mixture of propylene carbonate and dimethoxyethane. The polymer electrolyte comprises a polymer composition (20 wt %), a liquid electrolyte (78 wt %), and a photoinducer (2 wt %). Effect of insertion of dibenzo-18-crown-6 into the electrolyte on its electrochemical characteristics (on the electrolyte/Li interface) is investigated. Dependences of the bulk conductivity and exchange currents at the interface on the temperature and storage duration are studied at different crown ether contents.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 646–650.Original Russian Text Copyright © 2005 by Yarmolenko, Efimov.