Ion transport behavior in a new fast Ag ion conducting composite electrolyte system: 0.85[0.75AgI:0.25AgCl]:0.15CeO2

Investigations on ion transport behavior of a new fast Ag⁺ ion conducting composite electrolyte system: 0.85[0.75AgI:0.25AgCl]: 0.1CeO₂ are reported. An alternate host: ‘[0.75AgI:0.25AgCl] mixed system/solid solution’ has been used as first-phase host matrix salt, in place of the traditional host AgI, while the micron-size particles of an insulating and chemically inert CeO₂ as second-phase dispersoid. The soaking time, plays important role in determining the conductivity enhancement in the composite system. The system: 0.85[0.75AgI:0.25AgCl]:0.1CeO₂ prepared at soaking time ∼10 min. exhibited optimum conductivity:σ_rt ∼ 1.2 × 10⁻³ S cm⁻¹ at room temperature, which is an order of magnitude higher than that of the pure host. Structural characterization studies were performed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Temperature dependent measurement on the basic ionic parameters viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n), room temperature ionic transference number (t_ion) and ionic drift velocity (v_d) have been carried out on the system.     

Ion transport studies in CuI-doped silver borovanadate glassy system

In the present report, ionic transport properties and microstructural investigations of superionic materials in a cost-effective glassy system xCuI–(100 ? x)[2Ag₂O–0.7V₂O₅–0.3B₂O₃], where x = 30, 40, 45, 50 and 60, have been described. The temperature dependent electrical conductivity studies were carried out by ac impedance analysis. The microstructure of the materials studied by SEM indicated the presence of dispersed CuO and AgI micro-crystals in the silver oxysalt glass matrix. High room temperature electrical conductivity of 3.58 × 10^?3 S cm^?1 and low activation energy of 0.24 eV were obtained for the best conducting composition. The ac impedance data were analyzed using impedance and modulus formalisms. These materials show extremely high t_i value of 0.999 and the ionic conductivity is apparently due to Ag⁺ ions only. The use of two glass formers helped to form materials with higher T_g, higher thermal stability and better ionic transport properties.     

Transport property and structural characterization studies on (1 − x)[0.75AgI:0.25AgCl]:xTiO2 conducting composite electrolyte system

Transport property and structural investigation have been carried out on newly synthesized Ag⁺ ion conducting composite electrolyte system. The composite electrolyte system (1 − x)[0.75AgI:0.25AgCl]:xTiO₂, where 0 ? x ? 0.5 (in molar weight fraction) has been synthesized by melt quenching and annealing methods. The chemical compound TiO₂ (second phase dispersoid) dispersed in different compositions in a quenched (0.75AgI:0.25AgCl) mixed system/solid solution; this solid solution was used as a first phase host salt in place of AgI. The different preparation routes were adopted for the composite electrolyte system. Composition x = 0.1 exhibited highest conductivity at room temperature. The composite system 0.9[0.75AgI:0.25AgCl]:0.1TiO₂ was synthesized at different soaking times by melt quenching method. The system exhibited optimum conductivity at 20 min soaking time (σ_rt ≈ 1.4 × 10⁻³ S/cm). The ac conductivity has been measured from Z′-Z″ (Cole-Cole) complex impedance plots using impedance spectroscopic (IS) technique. The electrical conductivity as a function of temperature and frequency has been studied, and activation energy E_a, was calculated from Arrhenius plots for all compositions (0 ? x ? 0.5). The dc conductivity value has been evaluated from Log σ vs. log f plots. Structural characterization studies were carried out by X-ray diffraction (XRD) and differential thermal analysis (DSC) techniques.     

Conductivity and dielectric studies on 20CdI2–80[xAg2O–y(0.7V2O5−0.3B2O3)] super ion conducting system where 1 ⩽ x/y ⩽ 3

The present paper reports the conductivity and dielectric studies of the quaternary super ionic conducting system 20CdI₂–80[xAg₂O–y(0.7V₂O₅−0.3B₂O₃)], to see the effect of modifier to former ion ratios. The observed frequency dependence of conductivity is found to obey Jonscher’s universal law. The dc conductivity obtained from the low frequency part of the conductivity spectrum is found to be non-linear with change in the x/y ratio. Frequency and temperature dependence of the dielectric constant can be explained by Stevel’s model for dielectric relaxation in glasses. The conductivity and dielectric studies suggest that ionic motion in the system is responsible for the conductivity and relaxation effect. The silver ion transport number (t_Ag+) in the CdI₂ doped system is obtained by emf technique.     

A study of a fast ionic conductor–Ag1−xCuxI

The Conductivity of AgI–CuI system has been studied. Two molar ratios of the system Ag_1–xCu_xI with x = 0.05 and 0.15 have been taken. The transition temperatures are observed with conductivity measurements.     

Electrical characterizations of silver chalcogenide glasses

We present a study of the electrical properties of silver chalcogenide glasses ‘40AgI’–30Ag₂S–30GeS₂, 45AgI–27.5Ag₂S–27.5GeS₂ and 50AgI–25Ag₂S–25GeS₂ in the 77–400 K temperature and the 20 Hz to 1 MHz frequency ranges. In our temperature range, a large variation of the real permittivity is observed, in relation with an electrodes polarization effect. As the amount of silver iodide increases in the Ag₂S–GeS₂ matrix, the glass transition temperature and the activation energies decrease, the electrical conductivity increases and reaches 4 Ω⁻¹ m⁻¹ at room temperature for the glass with 50% AgI. The study of the conductivity shows a behavior due to a high ionic conductivity, thermally activated with E_dc = 0.21 eV, E₁ = 0.075 eV (40AgI–30Ag₂S–30GeS₂, 45AgI–27.5Ag₂S–27.5GeS₂), E_dc = 0.17 eV, E₁ = 0.055 eV for 50AgI–25Ag₂S–25GeS₂. For these glasses, we have seen three conductivity regimes. The first two terms are thermally activated. The third term cannot be actually clearly identified because either it is thermally activated with a very low activation energy and frequency dependent, or it is almost non-thermally activated and frequency dependent.     

The AC conductivity of superionic conducting glasses (AgI)x−(Ag4P2O7)1−x (x = 0.8, 0.75, 0.7): Experiment and analysis based on the generalized Langevin equation

The frequency-dependent complex impedance of superionic conducting glasses (AgI)_x − (Ag₄P₂O₇)_1−x (x = 0.3, 0.25, 0.20) was measured from 5 Hz to 500 kHz below room temperature. The frequency dependence of the conductivity and the electric modulus observed here cannot be expressed by a single relaxation equation, but it is well described by an equivalent circuit involving a contribution due to Jonscher's universal law σ [ω] ∼ ωⁿ (0 < n < 1). A linear relation between the DC conductivity and the relaxation time was observed irrespective of the sample compositions. These results are explained on the basis of the generalized Langevin equation associated with a non-exponential memory function. The physical basis of this approach is discussed in terms of the distribution of transition times arising from non-periodic potentials formed by immobile anions and many-body interactions among mobile cations at very high concentration in the superionic conducting glass.     

Crystallization and glass transition kinetics in Cu ion substituted Cux-Ag1 − xI-Ag2O-V2O5 superionic glasses

Crystallization kinetics and thermal properties in superionic glasses Cu_xAg_1 − xI-Ag₂O-V₂O₅ for x = 0.1-0.3 have been thoroughly investigated. X-ray diffraction and differential scanning calorimetry measurements confirm the precipitation of at least three compounds during crystallization, viz. AgI, Ag₄V₂O₇ and Ag₈I₄V₂O₇. The activation energies for structural relaxation (E_s) and crystallization (E_c) obtained using Moynihan and Kissinger formulation exhibit interesting trends with CuI substitution. The E_s value decreases with CuI substitution in the system. Further, the E_c values corresponding to precipitation of Ag₄V₂O₇ and Ag₈I₄V₂O₇ exhibit increasing trend, whereas, for that of AgI precipitation a decreasing trend with CuI content. The Avrami parameter calculated from Augis-Bennett method and Ozawa equation suggests predominantly surface crystallization in the glassy system. The electrical conductivity-temperature (σ-T) cycles interestingly demonstrate increasing precipitation of AgI with CuI content in the glass matrix.     

Medium range structure and power law conductivity dispersion in superionic glasses

The relationship between the exponent of the power law behavior in the ac conductivity and the wave number of first sharp diffraction peak (FSDP) in superionic glasses has been studied. For the case of (AgI)_x(AgPO₃)_1?x glasses, it is shown that the exponent of the power law increases with the decrease of the FSDP wave number. Other superionic glasses such as (AgI)_0.2(0.6Ag₂O–0.4V₂O₅)_0.8 and (AgI)_0.75(Ag₂MoO₄)_0.25 follow this trend. The relationship found is explained by using the energy barrier profile for the mobile ions in a disordered structure. The local energy barrier for the ion movement is determined by the local structure and bonding, and the ions flow through the low energy barrier sites. According to the model, the exponent of the power law contains information about the degree of connectivity of these low energy sites that extend at the intermediate length scale. The result suggests also that the universal aspect of the power law reflects the universal pattern of the potential barrier at intermediate length scales.     

Infrared spectra and structure of superionic conducting glasses in the system AgIAg2OMoO3

Thin blown films of glasses with the mole ratio Ag₂O/MoO₃ = 1 in the system AgIAg₂OMoO₃ (or the pseudobinary system AgIAg₂MoO₄) show three absorption bands in the range 4000-200 cm^?1; 875 cm^?1 (w), 780 cm^?1 (s), and 320 cm^?1 (m, b), which are characteristic of tetrahedral MoO₄^2? ions. The glasses with the ratio Ag₂O/MoO₃ < 1 have two additional bands at 600 cm^?1 (w) and 450 cm^?1 (vw), which are characteristic of condensed ions of MoO₄ tetrahedra, probably Mo₂ O₇^2? ions. These glasses are thus composed of Ag⁺, I^?, MoO₄^2?, and probably Mo₂O₇^2? ions, and classified as “ionic” glasses containing one type of cations. The presence of partial covalency in the Ag⁺… ^?OMo link and the influence of ion exchange of Ag⁺ with K⁺ on IR spectra are discussed. The molar volume of the glasses with the ratio Ag₂O/MoO₃ = 1 is primarily determined by a fairly dense packing of the constituent anions, I^? and MoO₄^2?.     

Fast ion conducting phosphate glasses and glass ceramic composites: Promising materials for solid state batteries

Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15 wt.%) were synthesized by melt quenching technique. The Ag₂O–P₂O₅–(15 wt.%) LiCl glass exhibited the maximum electrical conductivity (σ = 8.91 × 10^? 5 S cm^? 1 at room temperature and 4.16 × 10^? 3 S cm^? 1 at 200 °C). Using this glass as an amorphous host material, glass–ceramic composites of Ag₂O–P₂O₅–(15 wt.%) LiCl:xAl₂O₃ (x = 5–50 wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag₂O–P₂O₅–(15 wt.%) LiCl:(25 wt.%) Al₂O₃ composite system exhibited the maximum σ value (σ = 3.32 × 10^? 4 S cm^? 1 at room temperature and 2.88 × 10^? 2 S cm^? 1 at 200 °C ). Solid‐state batteries using undoped Ag₂O–P₂O₅ glass, Ag₂O–P₂O₅–(15 wt.%) LiCl glass and glass ceramic composite containing 25 wt.% Al₂O₃ as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics.     

A study on mixed conducting property of LixV2O5 (x = 0.4–1.4)

The mixed conducting nature of the lithium vanadate Li_xV₂O₅ (x = 0.4 – 1.4) prepared by solid state reaction has been analyzed by Wagner's polarization method. The increase of electronic conductivity with increase in lithium content has been observed. The low diffusion constant has been observed for lithium ionic motion in high lithium content samples. The conductivity spectra analysis shows the high columbic repulsive forces between mobile lithium ions in high lithium content samples. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Short range order and glass transition in AgIAg2OB2O3 vitreous electrolytes

Several experimental techniques are used to study the short range order, the dynamics and the glass transition in AgIAg₂B₂O₃ compounds. Addition of Ag₂O to B₂O₃, up to [Ag₂O]/[B₂O₃] ?0.5 modifies the borate network by creating a BO₄ unit for each silver added. Addition of AgI decreases the glass transition temperature (T_g) but has only minor effects on the short range structure of the borate network. Silver iodide is partially accomodated in the interstices of the glass network. The relationship among a tentative structural picture, the ion transport phenomena and the low temperature dynamics are discussed.An investigation of the dynamics in the AgI·Ag₂O·2B₂O₃ glass near and above T_g is presented. With NMR techniques, we monitor the onset of tumbling of the borate units and the dynamical effects of crystallization and/or aging of the glass. Hysteresis effects in the ionic conductivity (σ) temperature dependence and the non-Arrhenian behavior of σT near T_g are interpreted in terms of structural modifications occurring at elevated temperatures in the glass.     

Ion transport through LiCoO2/(Li2O)x · (B2O3) thin-film bi-layers

e-Gun deposited bi-layer structures of LiCoO₂/(Li₂O)_x · (B₂O₃) cathode material and solid electrolyte have been investigated by SEM and impedance spectroscopy. The crystallinity of the substrates, on which the structures are deposited, influences the extent of crystallization, and consequently the ionic conductivity, of the electrolyte layer. Comparison of impedance spectra between bi-layers and electrolyte single layers indicates that the total ionic conductivity of the electrolyte in the bi-layer is decreased with respect to the single layer, due to higher crystallization.     

Study of ion transport in Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript> solid electrolytes with different lithium isotope ratios

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li₂ZrO₃ solid electrolytes with different ⁶Li and ⁷Li ratios. It is found that single-isotope electrolytes undergo a transition to the superionic state in the temperature range of 430–450 K, accompanied by an abrupt increase in conductivity. As a result of introduction of the other type of the isotope, the conductivity jump disappears in this temperature range. The transition to the superionic state is attributed to the redistribution of lithium ions over energetically nonequivalent lattice sites.     

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li₂S-based sulfide and oxysulfide systems. The Li₂S–P₂S₅ glass–ceramics showed ionic conductivity as high as 3.2 × 10^?3 S cm^?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P₂S₅ glassy electrode and the Li₂S–P₂S₅ glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network.     

Growth and defect structure of CdF2 crystal and nonstoichiometric Cd1−x R x F2+x phases (R are rare earth elements and in): 6. Growth and ionic conductivity of Cd0.904In0.096F2.096 single crystal

Cd_0.904In_0.096F_2.096 crystals with fluorite-type defect structures have been grown from melt in a fluorinating atmosphere by the Bridgman method, and their ionic conductivity is investigated. The fluorine-ion transport activation enthalpy in Cd_0.904In_0.096F_2.096 (ΔH = 0.68 eV) is much smaller than the corresponding characteristic of the crystals belonging to the isoconcentration series Cd_0.9 R _0.1F_2.1, R = La-Lu, Y (ΔH = 0.8–0.9 eV). The ionic conductivity of Cd_0.904In_0.096F_2.096 is σ = 2 × 10^?4 S/cm (at 467 K); this value exceeds the conductivity of the CdF₂ crystal matrix and the highest conductivity Cd_0.9 R _0.1F_2.1 crystals with rare earth elements by factors of 3 × 10³ and ～10, respectively. Nonstoichiometric crystals of solid electrolyte Cd_{1 ? x} In _x F_{2 + x} have the highest conductivity out of all studied electrolytes based on the CdF₂ matrix.     

Study of ion transport behavior in a mechanochemically synthesized silver halide mixed composite system: [0.75 AgI:0.25 AgCl]

Ion transport behavior in a mechanochemically synthesized silver halide mixed composite has been investigated. AgI and AgCl, in 75: 25 mol. wt. (%) ratio, has been prepared by high energy ball milling for different milling times viz. 5, 10, 20, 30, 40, and 50 h as well as by simple physical mixing (referred to as zero hour milling). The room temperature conductivity has been evaluated as a function of milling time. The conductivity increased initially with increasing milling time, then decreased. The increase in conductivity has been attributed to the increased degree of amorphosity in the sample as a consequence of high energy ball milling. The 30-hour milled sample exhibited highest conductivity with an enhancement of more an order of magnitude from that of zero hour milled sample. To explain the ion transport mechanism in the optimum conducting sample, other basic ionic parameters viz. ionic mobility (μ), mobile ion concentration (n), ionic transference number (t_ion) etc. have also been determined. The materials and structural properties have been characterized using XRD, FTIR, and DSC techniques. Using the optimum conducting sample as electrolyte, all-solid-state battery has been fabricated having cell configuration: Ag (anode) // (0.75 AgI:0.25AgCl) // C + I₂ + Electrolyte (cathode), and the cell performance has been studied under varying load conditions.     

Addition effects of bismuth oxide on Samaria-doped ceria based lithium carbonate composite electrolytes for intermediate temperature-solid oxide fuel cells

ABSTRACT

The effect of amounts (3, 5, 10, 20 wt%) of Bi₂O₃ on the sintering characteristics and porosity of Samaria-doped Ceria (SDC) based Lithium carbonate has been evaluated. The density had a maximum as high as 98.5% of theoretical density at 800°C with only 1wt%Li₂CO₃ and 3 wt%Bi₂O₃. The composite electrolytes showed high ion conductivity at evaluated temperatures. Composition and calcination temperature were found to affect the morphology and conductivity of the composite electrolytes greatly. The total conductivity closed to 3 orders of magnitude greater than pure SDC at operating temperature of 900°C and 3.5 orders of magnitude greater than pure SDC at operating temperature of 600°C. Especially, the best sample containing 3 wt% Bi₂O₃ sintered at 800°C for 2 h which had an ionic electrical conductivity of 0.17S cm^?1. According to fuel cell performance, these composite electrolytes are chemically stable, which is an attractive prospect in intermediate temperature solid oxide fuel cell applications.     

Lithium rich phosphate glass: Crystallization kinetics,structural and conduction characteristics

Crystallization kinetic studies of Li⁺ ion conducting mol% 60Li₂O–40P₂O₅ glass indicate a 2-dimensional crystal growth mechanism as compared to the 3-dimensional growth mechanism for LiPO₃ glass (mol% 50Li₂O–50P₂O₅). Spectroscopic studies reveal that the structures of these two glass compositions differ considerably resulting in different mechanisms for crystal growth. Isothermal ionic conductivity studies further support 2-dimensional crystallization in mol% 60Li₂O–40P₂O₅ glass. Above the glass transition temperature the ionic conductivity deviates from the usual Arrhenian temperature dependence due to the additional effect of the movement of the phosphate polymeric chains in the glass network. The ionic conductivity of the glass ceramic corresponding to the mol% 60Li₂O–40P₂O₅ glass behaves in an Arrhenian fashion with an activation energy of 1.21 eV, much higher than that of 0.77 eV for the glass. Further, it is established using canonical scaling that the mechanism for ionic conduction is temperature independent.