Showing papers on "Ionic conductivity published in 1991"

Bulk Conductivity and Defect Chemistry of Acceptor‐Doped Strontium Titanate in the Quenched State

Abstract: The grain bulk conductivity of acceptor-doped SrTiO3 ceramics was investigated by the impedance analysis method after quenching from high-temperature equilibria. The influence of the oxygen partial pressure during equilibration, PEqO2, is described in terms of a defect model for titanates. From a comparison between the experimental results and the predictions of this model, a predominant ionic conductivity is concluded for a wide PEqO2 range (approximately 10−11 to 105 Pa). The influence of the ionization energy of the acceptors and of possible defect association is discussed.

Ionic Conduction in Phosphate Glasses

Abstract: Ionic conductivity in phosphate glasses has been known for almost 30 years. Recently these glasses have been shown to exhibit some of the highest ionic conductivities ever reported. In many cases, because of their ease of preparation, low melting points, strong glass-forming character, and simple composition, phosphate glasses have been studied more than any other ionically conducting glasses. However, no single review has ever been made of these glasses with the purpose of correlating the apparent widely disparate values of conductivity that these glasses exhibit. In this review, the conductivities of phosphate glasses are examined considering new structural studies of them. A systematic comparison of the dependence of the conductivity on glass chemistry reveals that, similar to other glass families (silicates and borates for example), the conductivity maximizes when the cation environments in the glass are minimized in their charge density and maximized in their site proximity.

Stabilization of superionic α -Agl at room temperature in a glass matrix

Abstract: SINCE the discovery1 that the high-temperature phase of silver iodide (α-AgI) has an ionic conductivity comparable to that of the best liquid electrolytes, solid electrolytes have attracted wide interest. Possible applications of these materials range from solid-state batteries to electrochromic displays and sensors2. Although α-AgI displays conductivities of more than 10 S cm−1 (ref. 3), owing to the almost liquid-like mobility of Ag+ ions, the crystal transforms below 147 °C to the β-phase with a conductivity of only ∼10−5 S cm−1 at room temperature. Efforts to achieve good conductivities at lower temperatures have focused on the addition of a second component to AgI to form solid solutions or new compounds such as RbAg4I5 and Ag2HgI4 (refs 4–7). Here we report our success in depressing the α→β transformation temperature so as to stabilize α-AgI itself at room temperature. We use a melt-quenching technique to prepare crystallites of α-AgI frozen into a silver borate glass matrix. The quenched material showed diffraction peaks characteristic of α-AgI and displayed ionic conductivities of about 10−1S cm−1. Further development of these glass/crystal composites may make the high ionic conductivity of α-AgI available for room-temperature solid-state applications.

A structural basis for ionic diffusion in oxide glasses

Abstract: The relationships between the environments of cations in alkali silicates measured by X-ray absorption fine structure (XAFS) and magic angle spinning nuclear magnetic resonance (MASNMR) are considered. Both are consistent with the modified random network for glass structure in which modifiers form channels percolating through the network. It is proposed that the mechanisms determining the distribution of bridging and non-bridging oxygen atoms at the glass transition are the same as those that promote ionic transport at lower temperatures in the glass. In particular the results of XAFS and MASNMR can be used to predict the activation energy for ionic transport and the magnitude of the electrical conductivity. Values of these parameters for alkali disilicates are in good agreement with those measured directly from transport properties.

Volume Effect or Paddle‐Wheel Mechanism—Fast Alkali‐Metal Ionic Conduction in Solids with Rotationally Disordered Complex Anions

Abstract: Transport phenomena in the solid state are of equal importance in basic research and practice. In the past two decades particular interest has been directed towards so-called “fast” or “super” ionic conductors because of their attractive potential applications. We have synthesized highly conductive alkali-metal ionic conductors based on ionic crystals in which, on the one hand, high concentrations of the charge carriers can be realized by doping (point defects in the cation substructure) and, on the other, the activation energy of the interchange of sites is decreased by translationally fixed but rotationally mobile complex anions. Mixed crystals with Na3PO4 or Na3AlF6 structures have proven especially suitable in this connection. With the object of establishing a broader experimental foundation for clarifying the controversially discussed question of whether the higher free transport volume or the rotational motion of the anions is responsible for the high cation mobility in these rotary phases we have systematically varied the type of anions and concentration of defects and monitored the resulting changes in conductivity. Although the macroscopical characteristics investigated are not suitable for explaining mechanisms in detail at the atomic level, the results afford clear support for the assumption of a “paddle wheel mechanism”; but also effects of the enlarged transport volume are not to be disputed. Both these effects enhancing the cationic conductivity are concomitantly operative in amounts varying from system to system; they cannot be totally separated from each other. Seen in this light, the alternative, “volume effect” or “paddle wheel mechanism,” is not as sharply defined as was previously discussed.

Ionic Transport in Oxide Glasses and Frequency Dependence of Conductivity

Abstract: Current models attribute the power law frequency dependence of ionic conductivity in oxide glasses alternatively to structural disorder or to interactions between moving ions. To distinguish between the influence of disorder and of interaction the frequency dependence of conductivity was investigated for three different series of glasses that have been selected according to special considerations on network structure and bonding of alkali ions. It was shown that the frequency response is independent of alkali concentration and structure. This result is discussed in terms of Coulomb interactions between mobile charged point defects and favours the jump relaxation model of Funke.

Solid electrolyte, electrochemical device including the same and method of fabricating the solid electrolyte

Abstract: A solid electrolyte with excellent ionic conductivity, which is composed of a viscoelastic material having a structure of a polymerized material and a non-aqueous electrolytic solution contained in the polymerized material, a chemical element containing the solid electrolyte, and a method of fabricating the solid electrolyte are described. This solid electrolyte contains the non-aqueous electrolytic solution in an amount of 200 wt. % or more of the polymer and has a modulus of elasticity of 102 to 105 dyne/cm2, and an elongation of 20% or more.

The system Y2O3―Sc2O3―ZrO2 : phase stability and ionic conductivity studies

Abstract: The ionic conductivity of the system Y2O3-Sc2O3-ZrO2 has been investigated, as a function of temperature (400–1000°C) and time (at 1000°C), for a range of Y/Sc ratios (eight compositions) at a constant dopant level of 8 mol%. The conductivity of scandia-rich compositions was almost twice that of the fully stabilized Y2O3-ZrO2 but in all the specimens the conductivity deteriorated with time on annealing at 1000°C. In Sc2O3-rich compositions, a dopant-rich t′-phase is formed by diffusionless transformation from the cubic phase on cooling the ceramic from the sintering temperature. On annealing at 1000°C, this phase decomposes to low-dopant t-ZrO2 precipitates and a cubic zirconia solid-solution matrix. In Y2O3-rich compositions only the cubic phase is formed but this is not an equilibrium phase with respect to dopant distribution. On annealing a slight redistribution of the dopant level and precipitation of t-ZrO2 takes place. These changes in the microstructure are responsible for the observed conductivity ageing process. The decrease in the conductivity and increase in the activation energy with increasing Y2O3 above 850°C has been discussed in terms of the steric blocking effect of the larger Y3+ cation.

Dielectric and conductivity relaxation in poly(propylene glycol)-lithium triflate complexes

Abstract: The electric modulus representation is used to display conductivity and dielectric relaxation occurring in poly(propylene glycol)‐4000 (PPG) complexed with LiCF3SO3, as the ether oxygen to lithium (O:Li) ratio is varied from 300:1 to 12:1. The frequency range covered is 10 to 107 Hz. Results are obtained for temperatures above the glass transition temperature appropriate for each PPG–LiCF3SO3 complex. For O:M=300:1, the conductivity peak and the α and α’ relaxation are clearly resolved. As the concentration is increased, there is a coupling between the structural and the conductivity relaxations; the various peaks begin to overlap. The coupling is greatest for an O:Li ratio in the range 30:1 to 12:1, where the highest conductivity is measured. Below room temperature, the 30:1 complex has the highest conductivity, above room temperature the 12:1 complex has the highest. At any particular temperature there is a concentration above which the conductivity drops. This drop is due to reduced ion mobility result...

DC Conductivity of Li1.3Al0.3Ti1.7(PO4)3 Ceramic with Li Electrodes.

Abstract: The ionic conductivity of a solid electrolyte, Li1.3Al0.3Ti1.7(PO4)3, was measured with Li and Li–Al alloy electrodes. The contact resistance between the Li electrode and the electrolyte was a dominant factor for the DC conductivity. A higher DC conductivity was obtained by an utilization of the Li4Al alloy electrodes.

A lithium-ion conducting solid electrolyte

Abstract: A lithium-ion conducting solid electrolyte of the present invention comprises a parent material, a lithium-ion conducting sulfide glass represented by the formula Li 2 S--X (X is at least one sulfide selected from the group consisting of B 2 S 3 , SiS 2 , P 2 S 5 , Al 2 S 3 , and GeS 2 ), and a high-temperature lithium-ion conducting compound (i.e. Li 3 PO 4 or Li 2 SO 4 ). The lithium-ion conducting solid electrolyte has higher ionic conductivity and higher decomposition voltage compared to the parent material. By the use of this solid electrolyte for electrical/chemical components such as batteries, condensers, electrochromic displays, and the like, electronic apparatus that includes such elements may have improved performance.

Ionic Conductivity of the Fluorite‐Type Hafnia–R2O3 Solid Solutions

Abstract: The ionic conductivity of the hafnia-scandia, hafnia-yttria, and hafnia-rare earth solid solutions with high dopant concentrations of 8, 10, and 14 mol% was measured in air at 600° to 1050°C. Impedance spectroscopy was used to obtain lattice conductivity. A majority of the investigated samples exhibited linear Arrhenius plots of the lattice conductivity as a function of temperature. For all investigated dopant concentrations the ionic conductivity was shown to decrease as the dopant radius increased. The activation enthalpy for conduction was found to increase with dopant ionic radius. The fact that the highest ionic conductivity among 14-mol%-doped systems was obtained with HfO2─Sc2O3 suggested that the radius ratio approach should be used to predict the electrical conductivity behavior of HfO2─R2O3 systems. A qualitative model based on the Kilner's lattice parameter map does not seem to apply to these systems. For the three systems HfO2─Yb2O3, HfO2─Y2O3, and Hf2O3─Sm2O3 a conductivity maximum was observed near the dopant concentration of 10 mol%. Deep vacancy trapping is responsible for the decrease in the ionic conductivity at high dopant concentrations. Formation of microdomains of an ordered compound cannot explain the obtained results. A comparison between the ionic conductivities of doped HfO2 and ZrO2 systems indicated that the ionic conductivities of HfO2 systems are 1.5 to 2.2 times lower than the ionic conductivities of ZrO2 systems.

Cationic Conductivity of Blend Complexes Composed of Poly[oligo(oxyethylene) methacrylate] and the Alkali Metal Salts of Poly(sulfoalkyl methacrylate)

Abstract: Two kinds of alkali metal salts of poly(sulfoalkyl methacrylate)s (PSAMM) were prepared, with which the blend complexes of poly[oligo(oxyethylene) methacrylate] (PMEOn) were formed. These blend complexes contain neither organic plasticizer nor low molecular weight Li-salt and are considered to be single-cationic conductors which are characterized by stable dc ionic conductivity. Cationic conductivity is deeply influenced by the glass transition temperature, cation species, polar group (acrylonitrile), the concentration of polymeric salts, and the size of side-group in PSAMM. An optimum Li+-ionic conductivity of 1.1×10−6 S cm−1 at 25°C is obtained for the blend complex P(0.6MEO18−0.4AN)/P(0.5SHMLi−0.5AN) (AN, acrylonitrile; SHMLi, lithium sulfohexyl methacrylate) with O/Li=72.

Ionic transport in LiNbO 3

Abstract: The high temperature equilibrium conductivity (950 °C–1050 °C) of congruent LiNbO 3 can be resolved into two components: an electronic portion that is dependent on the oxygen partial pressure and an ionic portion that is pressure independent. It is shown that the two components can be obtained from an analysis of the total equilibrium conductivity measured as a function of oxygen partial pressure. The ionic transport number (fractional ionic conductivity) thus obtained is compared with that obtained from an oxygen concentration cell measurement. The two techniques are found to be in excellent agreement, confirming the experimental validity of the defect chemistry method. From the temperature dependence of the ionic conductivity, the activation energy (138 kJ/mol [1.43 eV]) for the ionic transport is obtained. The results are in good agreement with the value previously obtained for the oxygen chemical diffusivity.

Ionic conductivity of bulk, gels and solutions of perfluorinated ionomer membranes

Abstract: Perfluorinated ionomer membranes either sulfonated or carboxylated have been extensively studied in order to understand the relations between their structure and properties. In addition to their uses as separator in the Cl2/NaOH industry large potential applications exist in different fields like sensors, batteries, fuel cells, electrochromic displays, etc. Some of these applications are due to the possibility of getting solutions, gels from these materials in different solvents and of reconstructing membranes of different thicknesses. The aim of this presentation is to present conductivity measurements of solutions, gels and bulk membranes, which measurements are of primary interest for potential applications in electrochemical devices. Room temperature measurements of conductivity of solutions/gels: First of all we recall the results already published which show the high conductivity of these gels associated with a transport number t+=1 since the COO− or SO3− anions are covalently bound to the rigid perfluorinated rod like structure. Low temperature measurements: Polymers having ionic conductivity usually show drastic changes upon temperature associated to transition (Tg, Tm or sub Tg relaxations). Measurements of conductivity of NAFION® 1100 solutions in propylene carbonate or dimethoxyethane over a temperature range between +20°C and −40°C have shown only small changes mainly due to viscosity modifications of the solvent as evidenced from the calculated activation energies. Conductivity/swelling measurements: We have recently developed an experiment which permits to obtain both the conductivity and the swelling of ion exchange membranes. Equilibrium experiments with solvent mixtures permit to check the conductivity and swelling changes versus different parameters (dielectric constant of solvent, ionic radius of the counterion, etc.). Diffusion coefficients are also obtained from the time lag when immersing the membrane in the solvent.

Transport in ionic conducting glasses

Abstract: The frequency-dependent conductivity of glasses is explained in a treatment spanning the range of frequencies, 0< omega < nu ph approximately=1012 Hz. A large spread of individual relaxation times is assumed. The connection between low frequency AC conduction and DC conduction is their common origin in non-local relaxation processes. This connection has already been exploited to derive results for sigma ( omega ) in the electronic systems known as the Fermi glass and the 'electron glass', which are in quantitative agreement with experiment. In these systems, quantitative expressions are available for the distribution of relaxation times, in contrast to the situation in ionic conducting glasses. In ionic conducting glasses, as in the electron glass, the effects of Coulomb interactions in the sequential correlation of individual transitions is critical at low frequencies when the relaxation is non-local. The framework of the calculations is given by percolation theory.

Low Temperature Limiting‐Current Oxygen Sensors Based on Tetragonal Zirconia Polycrystals

Abstract: This paper reports that yttria doped tetragonal zirconia polycrystals can overcome the phase transition into the monoclinic phase at about 500{degrees} C and show higher ionic conductivities than cubic stabilized zirconia in spite of the lower defect concentration. This material is applied in oxygen gas sensors under limiting current conditions at intermediate and ambient temperatures. AC and dc conductivities, Tafel behavior, minority charge carrier diffusivity, and the i-V characteristics are reported. The detection limit of the oxygen partial pressure and the response time depend on the thickness of the electrolyte and are related to the oxygen ion conductance and the electronic mobilities, respectively. The sensors may be optimized by the application of thin film electrolytes and of modified configurations with solid oxide bulk conducting diffusion barriers.

Ionic conductivity studies on salt-polyzwitterion systems

Abstract: Zwitterionic polymers of the sulfobetaine type and with various structures are studied. Salts used include LiI, LiClO 4 and LiBPh 4 at several concentrations (0-1 M). Variations of conductivity with temperature follow an Arrhenius behavior, with values found within the range from 10 -6 to 10 -4 S cm -1 . Dielectric relaxation studies showed a Debye-type behavior within 0.2-0.8 M salt concentration and significant deviations for the pure polymer and the equimolar mixture

Mixed (electronic and ionic) conductive solid polymer matrix, 1. Synthesis and properties of poly(2,5,8,11,14,17,20,23-octaoxapentacosyl methacrylate)-block-poly(4-vinylpyridine)

Abstract: Poly(2,5,8,11,14,17,20,23-octaoxapentacosyl methacrylate)-block-poly(4-vinylpyridine) semicomb polymers were synthesized using anionic living polymerization techniques. The polymers are white, powdery materials and were characterized by 1H and 13C nuclear magnetic resonance spectroscopy and gel-permeation chromatography. The polymers display monomodal molecular weight distributions which are relatively narrow. The block copolymers show microphase separation as indicated by the presence of two glass transition temperatures (Tg), a soft (oxyethylene) phase Tg is observed between −60°C and −45°C and a hard (4-vinylpyridine) phase Tg is observed between 135°C and 150°C. The soft oxyethylene phase has been doped with LiClO4 to obtain ionic conductors with electrical conductivities around 5 · 10−6 S · cm−1 at 25°C and the hard 4-vinylpyridine phase has been complexed with 7,7,8,8-tetracyano-1,4-quinodimethane (TCNQ, 2,5-cyclohexadiene-1,4-diylidenedimalonitrile) to obtain electronic conductivities around 10−6 S · cm−1 at 25°C. The mixed (electronic and ionic) conductivities are intermediate between the ionic and electronic conductivities. Higher electronic conductivities (≈ 10−5 S · cm−1 at 30°C) are obtained for the polycation TCNQ−/TCNQ0 complexes.