Showing papers on "Ionic conductivity published in 1982"

Vibrational Spectroscopic Determination of Structure and Ion Pairing in Complexes of Poly(ethylene oxide) with Lithium Salts

Abstract: A structural model for crystalline complexes of poly(ethylene oxide) (PEO) with various lithium salts is presented, based on vibrational spectroscopic studies; these complexes are known to exhibit ionic conductivities of > 10 -/sup 5/ (/OMEGA/-cm)-/sup 1/ at 100/sup 0/C. Cation-dependent vibrational bands observed in the Raman indicate that significant cation-oxygen atom interactions occur and suggest that the polyether chain may wrap around the lithium cations. Spectroscopic studies indicate extensive contact ion pairing occurs in the PEO*LiNO/sub 3/ complex, and this may contribute to the somewhat lower ionic conductivity of this complex as compared to other lithium salt complexes with similar structures but weaker cation-anion interactions. 27 refs.

Conformation and Ion‐Transport Models for the Structure and Ionic Conductivity in Complexes of Polyethers with Alkali Metal Salts

Abstract: Two ion‐transport mechanisms are described for ion transport in polyether‐alkali metal salt complexes: an intrahelical jumping process along crystalline (helical) regions of the polymer, and a transport process in the amorphous regions which is dependent on formation of fourfold coordination sites via mutual motion of ether oxygens from two or more polymer chains. The intrahelical jumping process may exhibit Arrhenius behavior, while transport in the amorphous regions should behave like a configurational entropy dominated process, showing a temperature dependence like , where is the equilibrium glass transition temperature. For the highly crystalline poly(ethylene oxide) complexes, an Arrhenius behavior is observed to dominate, whereas for the amorphous polyether salt complexes the configurational entropy behavior is observed. Even for the highly crystalline complexes, however, amorphous regions separate the crystalline regions of the polymer, and segmental motion of the polymer chains is postulated to be crucial here as well. The models are consistent with the observed frequency‐dependent ionic conductivity, as well as spectroscopic, x‐ray, thermal, and physical characterization measurements. They provide a reasonable microscopic picture for ion motion and yield testable predictions concerning the dependence of the ionic conductivity on pressure, temperature, and crystallinity.

Ionic conductivity of polyether‐polyurethane networks containing NaBPh4: A free volume analysis

Abstract: The ionic conductivity of polyoxyethylene- and polyoxypropylene-polyurethane networks containing sodium tetraphenylborate was studied as a function of temperature and salt concentration. The results can be rationalised in terms of free volume considerations. The fact that the WLF equation applies to the conductivity of these materials demonstrates that there exists a direct relationship between the ion conduction process and the viscoelastic properties of the networks.

Short range order and glass transition in AgIAg2OB2O3 vitreous electrolytes

Abstract: 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 (Tg) 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 Tg 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 Tg are interpreted in terms of structural modifications occurring at elevated temperatures in the glass.

Oxygen probes based on calcia-doped hafnia or calcium zirconate for use in metallic melts

Abstract: Up to the present, fully or partially stabilized zirconia has been used as a solid electrolyte material in probes for the determination of oxygen in metallic melts. In the present study, the ionic conduction behavior of HfO2 (CaO) solid solutions and the compound calcium zirconate CaZrO2 have been investigated. Both polarization experiments and EMF measurements on oxygen concentration cells point out that these two highly refractory oxide materials are also most suitable solid electrolytes. Their use is particularly recommended for oxygen probe measurements in deoxidized steel melts where extremely high chemical stability and low partial electronic conductivity of the solid electrolyte is required. In the paper, properties such as crystal structure, free energy of formation, thermal expansivity, ionic and total electrical conductivity are summarized and compared for fully and partially stabilized ZrO2, calcium zirconate CaZrO3, HfO2 (CaO), and ThO2 (Y2O3) solid solutions.

Ionic conductivity of hybrid films based on polyacrylonitrile and their battery application

Abstract: The alternate current (AC) and direct current (DC) ionic conductivity of hybrid films composed of polyacrylonitrile (PAN), lithium perchlorate (LiClO4), and a plasticizer was studied. Three kinds of the plasticizer [ethylene carbonate (EC), propylene carbonate (PC), N,N-dimethylformamide (DMF)] were used. Suitability of these hybrid films for lithium battery was investigated. The AC conductivity, which represents bulk ionic conductivity, was dependent on the component and the composition of the hybrid films, ranging from 10−4−10−8 Scm−1. The AC conductivity was mainly determined by the molar ratio of [plasticizer]/[LiClO4] in the hybrid films and increased with the increase in this ratio. The effect of the plasticizer on the enhancement in the AC conductivity was in the following order. DMF>EC>PC. The hybrid films with both electrodes of lithium showed the stable DC conductivity of about 1/10 of the AC conductivity, except for the hybrid films containing DMF. The hybrid films were found to be effective as a lithium ionic conductor. The galvanic cell. Li/sample/MnO2, at the discharge current density of 90 μA/cm2 showed the stable electromotive force of about 3 V for 70 h.

Composite and flexible anodes for lithium cells in non-aqueous medium

Abstract: Anode composition based on a mixture of plastic or elastomeric macromolecular material with ionic conduction, an alloy of lithium and particles of a carbon compound of the formula: Li x C where 0≦x<0.3. Anodes so constituted, as well as electrochemical generators with solid electrolytes comprising these anodes. Better utilization of the lithium of the materials of the electrodes.

Temperature dependence of ionic conductivity in glass: Non-arrhenius behavior in the Ag7I4AsO4 system

Abstract: Rapidly quenched Ag7I4AsO4 glasses show an abnormal curvature in conductivity Arrhenius plots (log σT versus 1/T) in the region below the glass transition temperature. This curvature decreases progressively as the fictive temperature is lowered by annealing for extended periods below Tg, and ultimately “normal” linear behavior is observed when the annealing is carried out at a sufficiently low temperature. It is suggested that the curvature, which implies a temperature-dependent activation energy for the ionic motion, arises from a coupling between the motion of the mobile silver ions, and temperature-dependent local structural changes in the glass.

Solid electrolytes—the beta aluminas

Abstract: Electrolytes conduct electricity by the movement of ions, whereas metals conduct by the flow of electrons. Until recently, almost all electrolytes known to have high conductivities were liquids, such as molten salts or aqueous solutions of salts. But research over the last twenty years has uncovered many solid electrolytes—substances that have a high ionic conductivity even though they are insulators to the flow of electrons. Physicists often call these solids “superionic conductors” because a number of the compounds have electrical conductivities comparable with those of liquid electrolytes. (But we will avoid this term to prevent a possible mistaken identification with superconductors.)

Super ionic conductive glass

Abstract: An ionically conducting glass for use as a solid electrolyte in a power or secondary cell containing an alkali metal-containing anode and a cathode separated by an alkali metal ion conducting glass having an ionic transference number of unity and the general formula: A 1+x D 2-x/3 Si x P 3-x O 12-2x/3 , wherein A is a network modifier for the glass and is an alkali metal of the anode, D is an intermediate for the glass and is selected from the class consisting of Zr, Ti, Ge, Al, Sb, Be, and Zn and X is in the range of from 2.25 to 3.0. Of the alkali metals, Na and Li are preferred and of the intermediate, Zr, Ti and Ge are preferred.

Ionic conductivity of polymeric solid electrolytes based on poly(propylene oxide) or poly(tetramethylene oxide).

Abstract: Ionic Conductivity of Polymeric Solid Electrolytes Based on Poly(propylene oxide) or Poly(tetramethylene oxide)

Influence of Annealing on the Electrical Conductivity of Polycrystalline ZrO2+8 Wt% Y2O3

Abstract: Solid electrolytes of zirconia are used in electrochemical cells, fuel cells and for monitoring of oxygen in metals. The electrical conductivity of partially stabilized zirconia was investigated as a function of frequency (2 Hz to 100 kHz) and temperature (400/degree/to 1000/degree/C) by measuring ac admittance on a 2-probe cell using Lissajous figures. The dependence of the conductivity on annealing time was investigated with in situ conductivity measurements for prolonged annealing at 800/degree/, 900/degree/, and 1000/degree/C. The aging behavior of two commercial zirconias was studied. 20 refs.

A SCRF‐CNDO/2 study on proton conductivity mechanisms in hydronium perchlorate. Towards a quantum chemical representation of defects and impurities in crystals

Abstract: A quantum chemical scheme adapted to study charge separation processes in crystalline molecular/ionic defects is presented. The scheme derives from a generalized self‐consistent reaction field theory of surrounding medium effects. Computational implementation has been done at the CNDO/2‐INDO approximate level; lattice sums are performed by direct summation techniques. The sums are essential for building the static dielectric response function of the crystal to the field set up by the defect charge density and the Madelung potential created by the surrounding crystal permanent charge density. The scheme has been applied to study some aspects of the proton conductivity mechanism in crystalline hydronium perchlorate. The theoretical results lend support to an experimentally grounded molecular mechanism. The theoretical scheme can easily be extended to describing chemical processes taking place at crystal surfaces.

Temperature dependence of electrical conduction of sodium-iron phosphate glasses

Abstract: The electric conductivity was measured from 150 K to 300 K on sodium-iron phosphate glasses having the composition of X Fe 2 + Y O 3 . (45 − X )Na 2 O·55P 2 O 5 ( X = 0−45, Y = 0.09–0.98) in which ionic and/or electronic conduction may be possible. The conduction mechanism was examined on the basis that the activation energy of electronic conducting glasses is generally lower than that of ionic conducting glasses, and the relation between the logarithm of conductivity and the reciprocal of temperature deviates from linearity at high temperatures ( T > θ D /2), θ D being the Debye temperature, due to the contribution of the variable-range hopping conduction. The results obtained are as follows: 1. (1) when X is less than 15, the electric behavior of the glass is similar to that of sodium phosphate glasses, which show the ionic conduction; 2. (2) when X is more than 15, the electric behavior of the glass is similar to that of iron phosphate glasses, which show electronic conduction; 3. (3) when X is 15, the transition of electric behavior depends upon the amount of Fe 2+ ions in the glass.

Crystal structures of fast ion conductors

Abstract: Fast ionic conductors are characterized by the rapid diffusion of ions through the crystal lattice. The mobile ion species move through the framework formed by all the other atoms. The positions of the framework atoms can usually be assigned to completely occupied atomic sites. The arrangement of the mobile ions within the ordered framework is frequently described as a molten sublattice. There exist two main reasons for assuming a "molten" state of the mobile ions in a crystalline framework. Firstly, for some ionic conductors [e.g. a-AgI (1)] the ionic conductivity is higher in the crystalline state than in the molten state. Secondly, crystal structure analyses have shown for several fast ionic conductors that the mobile ions occupy their sites with probabilities much lower than one (e.g. a-AgI or p-alumina). Frequently regular and interstitial sites are barely dis­ tinguishable. Such microscopic pictures of ionic conductors are derived from crystal structure analyses. These investigations are based on elastic neutron or x­ ray diffraction, in which the intensities of Bragg reflections are measured. A nuclear or electron average density can be calculated from these intensities by means of Fourier transformations. These periodic densities are then interpreted within the frame of a structure model. Nearly all structure investigations of ionic conductors are carried out with a so-called standard structure model, which uses several simplifications. The advantage of this standard structure model lies in the low number of structure parameters used to describe an experimental density. It allows, therefore, the rapid calculation of these structure parameters from rather limited data sets. Its disadvantage lies in the insufficient treatment of the thermal motion of the mobile ions, which may lead to a partly incorrect structure model for these ions.