Synthesis,structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers

Atomistic simulations have shown that the calculated conductivity of nano-polycrystalline BaF2/CaF2 heterolayers is considerably higher than the component bulk materials and we predict that grain-boundary diffusion is the key to fast ionic conductivity in these systems.     

Conductivity of CaF2-MgO composites

Conductivity of CaF₂-(20, 30, 40 vol %) MgO composites was measured as dependent on the temperature and MgO dispersion degree using a standard four-probe dc method. It is shown that the conductivity of composites grows at an increase in the MgO dispersion degree and volume fraction and achieves its maximum at 30 vol % MgO. It is found that the conductivity of CaF₂-30 vol % MgO nanocomposite is higher by two orders of magnitude as compared to pure CaF₂.     

Thermodynamics of ionic solid solutions: III. An addendum

In two earlier papers (C.A. 117:259320(1;121:19411y) the activity coefficients of the salts in binary solid solutions at 25‡C for 38 salt pairs, in which the members of each pair differ with respect to only one kind of ion, were determined. While the activity data are correct, the conclusions regarding deviations from ideality for eight of these pairs, namely those in which there are two moles of replaceable ion per mole of salt, require modification in order to be consistent with ideal entropies of mixing. By changing the formulation of the component salts to one-half of what is usual, the inconsistencies disappear. This half-mole approach, applied to the salt pairs CU_1/2(NH₄/K)SO₄-3H₂O, Mg_1/2NH₄(SO₄/ CrO₄)-3H₂O, Mg_1/2NH₄(SeO₄/SO₄)-3H₄O, Mg_1/2NH₄(SeO₄/CrO₄)-3H₄O, Mg_1/2 (K/NH₄)SeO₄-3H₂O, (NH₄/K)(SO₄)_1/2, and Ba_1/2(ClO₃/BrO₃)-1/2 H₂O shows that these solid solutions exhibit positive, not negative, deviations from ideality at 25‡C. Only the system Pb_1/2(C1/Br) still deviates negatively.     

Electric conductivity of nanocluster polyoxomolybdates in the solid state and solutions

The electric conductivity of nanocluster polyoxomolybdates (POMs) Mo₁₃₂ and Mo₇₂Fe₃₀ with a keplerate structure in aqueous solutions, of these POMs in the solid state, and of Mo₁₃₈ with a toroidal structure was studied. Data on the concentration dependence of the equivalent electric conductivity in solutions and on the specific conductivity of the solid samples were obtained. Solid Mo₁₃₂ showed predominantly electron type of conductivity at nearly room temperatures due to the presence of molybdenum at different oxidation levels; Mo₇₂Fe₃₀, which has metal components at the highest oxidation levels, was found to be poor electric conductor; Mo₁₃₈, which has a lower content of low-valence molybdenum than Mo₁₃₂, showed intermediate conductivity and a reversible transition between the proton and electron types of conductivity.     

Some factors responsible for high ionic conductivity in simple solid compounds

The ionic conductivities, activation energies for mobility, and crystal structures of solid electrolytes are reviewed. The high conductivity of a group of compounds containing simple anions is examined in some detail.For a solid to possess high ionic conductivity there must be: (a) an excess of acceptable lattice sites for the mobile ion, (b) only a small energy difference between the ordered and disordered distribution of the mobile ions over these sites, and (c) a low heat of activation for movement of the mobile ion. These conditions are most readily realized when the cations are monovalent and stable in both 4-coordinated (tetrahedral) and 3-coordinated configurations. Since only Ag^I and Cu^I satisfy these requirements, their nearly unique conduction properties become understandable. Moreover, these requirements appear to be satisfied only with highly polarizable anions; a characteristic of the anions present in the good conductors.     

Ionic conduction in glasses in the MnNbOF5-BaF2-BiF3 system

The electrical conductivity of oxyfluoride glasses in the MnNbOF₅-BaF₂-BiF₃ system in the temperature range 299–550 K was studied by impedance spectroscopy. It was shown that the conductivity is mainly caused by fluoride ions forming fluorobismuth polyhedra in the glass structure, being as high as 7.46 × 10^?3 S/cm (533 K) in the 20MnNbOF₅-30BaF₂-50BiF₃ system reaches, which is at the level of the best values for fluoride glasses.     

Optimization of ionic conductivity in solid electrolytes through dopant-dependent defect cluster analysis

Atomistic simulation based on an energy minimization technique has been carried out to investigate defect clusters of R(2)O(3) (R = La, Pr, Nd, Sm, Gd, Dy, Y, Yb) solid solutions in fluorite CeO(2). Defect clusters composed of up to six oxygen vacancies and twelve accompanied dopant cations have been simulated and compared. The binding energy of defect clusters increases as a function of the cluster size. A highly symmetric dumbbell structure can be formed by six oxygen vacancies, which is considered as a basic building block for larger defect clusters. This is also believed to be a universal vacancy structure in an oxygen-deficient fluorite lattice. Nevertheless, the accurate positions of associated dopants depend on the dopant radius. As a consequence, the correlation between dopant size and oxygen-ion conductivity has been elucidated based on the ordered defect cluster model. This study sheds light on the choice of dopants from a physical perspective, and suggests the possibility of searching for optimal solid electrolyte materials through atomistic simulations.     

Correction to: Lithium ion conductivity of solid solutions based on Li8ZrO6

Journal of Solid State Electrochemistry - Lithium ion conductivity of lithium hexaoxozirconate Li8ZrO6 doped by Mg2+, Sr2+, Nb5+, V5+, and Ce4+ cations was studied using impedance spectroscopy. The...     

Pseudolattice theory of charge transport in ionic solutions: Corresponding states law for the electric conductivity

A statistical mechanical framework for charge transport in ionic liquid–solvent mixtures based on the existence of a statistical lattice structure (pseudolattice) throughout the whole range of concentration is reported. The ion distribution is treated in a mean-field Bragg–Williams-like fashion, and the ionic motion is assumed to take place through hops between cells of two different types separated by non-random-energy barriers of different heights depending on the cell type. Assuming non-correlated ion transport, the electrical conductivity is shown to have a maximum, arising from the competition between the concentration of charge carriers in the bulk medium and their mobilities in the pseudolattice. An explicit expression for the concentration at which this maximum occurs is given in terms of microscopic parameters, and the electrical conductivity normalized by its maximum value (κ/κ_max) is shown to follow rather closely a universal corresponding states law in concentration space when represented against the ionic concentration scaled by its value at the conductivity maximum (?_α/?_max). Ion–ion and ion–solvent interactions are explicitly considered combining the path probability method for charge transport in solid electrolytes and the Bragg–Williams approximation for interparticle interactions, and their impact on the deviations of experimental data from the universal behavior of non-correlated transport analyzed. The theoretical predictions are shown to satisfactorily predict experimental values of electrical conductivity of aqueous solutions of conventional electrolytes and of mixtures of room temperature molten salts with typical solvents.     

Phase equilibria and modeling of ammonium ionic liquid, C2NTf2, solutions

Novel quaternary ammonium ionic liquid, ethyl(2-hydroxyethyl)dimethylammonium bis(trifluomethylsulfonyl)imide (C2NTf2), has been prepared from N,N-dimethylethanolamine as a substrate. The paper includes a specific basic characterization of the synthesized compound by NMR and the basic thermophysical properties: the melting point, enthalpy of fusion, enthalpy of solid-solid phase transition, glass transition determined by the differential scanning calorimetry (DSC), temperature of decomposition, and water content. The density of the new compound was measured. The solid-liquid or liquid-liquid phase equilibria of binary mixtures containing {C2NTf2+water or an alcohol (propan-1-ol, butan-1-ol, hexan-1-ol, octan-1-ol, decan-1-ol), aromatic hydrocarbons (benzene, toluene), aliphatic hydrocarbons (n-hexane, n-octane), dimethylsulfoxide (DMSO), or tetrahydrofuran (THF)} have been measured by a dynamic method in a wide range of temperatures from 230 to 430 K. These data were correlated by means of the nonrandom two-liquid (NRTL) equation utilizing temperature-dependent parameters derived from the solid-liquid or liquid-liquid equilibrium. From the solubility results, the negative value of the partition coefficient of ionic liquid in binary system octan-1-ol/water (log P) at 298.15 K has been calculated.     

From Composites to Solid Solutions: Modeling of Ionic Conductivity in the CaF2–BaF2 System

By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent “dopants” can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state‐of‐the‐art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF₂ lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF₂ phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF₂–BaF₂ multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge‐transfer that occurred at the hetero‐interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher‐dimensional doping) to homogeneous doping (zero‐dimensional doping).     

Properties of solid solutions in the KCl-NaCl system

Conditions for the decomposition of solid solutions in the KCl-NaCl system and their electrophoretic properties were studied. Compositions based on the KCl-NaCl system can be used for producing temperature sensors.     

Perovskite solid solutions in the BaO-CuO-Y2O3-Nb2O5 system

Freeze dried complex carboxylates are highly reactive precursors for complex perovskite solid solutions in the system BaO-CuO-Y₂O₃-Nb₂O₅ On thermal decomposition of the amorphous precursors the formation of complex crystalline phases begins at 600 °C. In most cases the themodynamically controlled phase composition is reached after a reaction time of two hours at about 900 °C. Beginning from the perovskite compound Ba₂YNbO₆ a partial substitution of Y by Cu or by a combination 2/3 Cu,1/3 Nb leads to extended fields of solid solutions with cubic perovskite structure. Substitution according to Y_0,5xBa₂(Y_1-0,5xCu_xNb)O_6+x is limited to x ≤ 0,4. A compound LBa₂Cu₂NbO₈ (x=2), well characterized for L=La, does not exist for L=Y. The composition of solid solutions depends on the preparation conditions. There are some signs for an inhomogeneous distribution of B-cations in the cubic perovskites.     

Phase diagram of the system CaF2-GdF3

A phase diagram of the system CaF₂-GdF₃ was studied by thermal and X-ray analysis. Two wide domains of solid solutions based on CaF₂ and a high-temperature modification of α-GdF₃ (LaF₃-structural type) are present in this system. Two maxima were found on the melting curves of the Ca_1?xGd_xF_2+x and α-(Gd_1?yCa_yF_3?y solid solutions, at 1428 ± 10? (5 mole % GdF₃) and 1282 ± 5? (85 mole % GdF₃), respectively. The coordinates of the eutectic are 60 mole % GdF₃ and 1233 ± 5?.

     

Electrolytic conductivity: a reference system for aqueous solutions

To establish a system for the measurement of electrolytic conductivity in aqueous solutions with traceability to the SI, a cell has been developed with a removable central section providing an accurate determination of the geometrical constant. As the concentration unit mass/mass, based and referred to the amount of substance in the SI, is recommended by international organisations, 0.1 molal KCl samples have been prepared and analysed. Results over a temperature range from 20 degrees C to 35 degrees C are presented. The main sources of error have been estimated and relative uncertainty has been assessed to remain at the level of 0.6%. Satisfactory agreement is observed when the results are compared with the reference values available from literature.     

Electrical conductivity of lithium chloride solutions in the propanol-water system

Electrical conduction of lithium chloride solutions in the propanol-water system was studied in the temperature range by using the conductometric method. The electrical conductivity of the solutions was determined in relation to the contents of water and lithium chloride.     

Conductivity of micellar solutions of ionic surfactants and surface conductivity of micelles

Within the effective medium model, a method is proposed for determining the surface conductivity of micelles. The known experimental data on the conductivity of aqueous sodium dodecyl sulfate micellar solutions are analyzed employing the developed approach. Specific surface conductivity λ_s of micelles is shown to be 10⁻⁸Ω⁻¹. The high values of λ_s are indicative of a noticeable contribution of the dense part of the electrical double layer, which is comparable with the contribution of its diffuse part, to the micellar solution conductivity. This estimate is strongly dependent on the initial information obtained in different studies. The marked influence of the micelle surface conductivity on the effective conductivity of micellar solutions allows one to put the question of the correctness of the method commonly used to determine the degree of counterion binding from the slopes of the dependences of the solution conductivity on the overall surfactant concentrations in the premicellar and micellar regions.     

Effect of bismuth trifluoride on the characteristics of fluoroindate glasses: The InF3-BiF3-BaF2 system

Glass formation in the InF₃-BiF₃-BaF₂ system is studied. Partial substitutions of BiF₃ for InF₃ in the InF₃-BaF₂ system reduce the glass-transition and glass-crystallization temperatures and increase the thermal stability range and refractive index. The glass structure is studied using IR and Raman spectroscopy. InF₆ and BiF_n polyhedra are identified in the system. Doping the glass with bismuth trifluoride changes the degree and linkage character of the InF₆ polyhedra in the glass network. The medium-range order length is not affected by the bismuth trifluoride concentration in the glass. The modifier cation (Ba²⁺) substantially determines the correlation length in the glasses.     

Electrical conductivity of solutions of the LiIO3-HIO3-H2O system

The electrical conductivity of aqueous LiIO₃ solutions and solutions of the LiIO₃-HIO₃-H₂O system is measured over a wide range of compositions at 25, 50, and 75°C. Isothermal surfaces of electrical conductivity are mapped, and the activation energies of conductivity are calculated. The conductivity isotherms in the LiIO₃-H₂O and HIO₃-H₂O boundary binary systems and in mixed solutions along sections with fixed electrolyte ratios each have a maximum as a function of electrolyte concentration. It is assumed that structure reorganization occurs in solutions in the concentration range corresponding to the peak conductivity. Proton migration features in the solutions in question are considered.