Showing papers on "Ionic conductivity published in 1979"

Physics of superionic conductors

Abstract: 1. Introduction.- References.- 2. Structure and Its Influence on Superionic Conduction: EXAFS Studies.- 2.1 Technique of EXAFS.- 2.1.1 Theory.- 2.1.2 Experiment.- 2.1.3 Data Reduction and Analysis.- 2.1.4 Contrast with Diffraction Studies.- 2.2 Structural Considerations for Superionic Conduction.- 2.2.1 General Considerations.- 2.2.2 Pair Potentials.- 2.2.3 Anharmonic Model.- 2.2.4 Excluded Volume Model and Cation-Anion Correlations.- 2.3 EXAFS Investigations of bcc Superionic Conductors: AgI.- 2.3.1 Early Structural Studies.- 2.3.2 EXAFS Study.- 2.3.3 Other Recent Structural Studies.- 2.3.4 Structural Model for Superionic Conduction in bcc Conductors.- 2.4 EXAFS Investigations of fcc Superionic Conductors: Cuprous Halides.- 2.4.1 CuI Structural Studies.- 2.4.2 EXAFS and Structural Models for CuI.- 2.4.3 CuBr.- 2.4.4 CuCl.- 2.4.5 Discussion.- 2.5 Summary.- References.- 3. Neutron Scattering Studies of Superionic Conductors.- 3.1 Neutron Scattering.- 3.1.1 Scattering function.- 3.1.2 Elastic Scattering.- 3.1.3 Inelastic Scattering.- 3.2 Structural Studies.- 3.2.1 AgI.- 3.2.2 Fluorites.- 3.2.3 ?-Alumina.- 3.3 Inelastic Studies.- 3.3.1 AgI.- 3.3.2 RbAg4I5.- 3.3.3 Fluorites.- 3.3.4 ?-Alumina.- 3.4 Conclusions.- References.- 4. Statics and Dynamics of Lattice Gas Models.- 4.1 General Theory of the Lattice Gas Model for Superionic Conductors.- 4.1.1 Definition of the Lattice Gas Model.- 4.1.2 Liouvillian Approach to Lattice Gas Dynamics.- 4.1.3 Master-Equation Approximation.- 4.1.4 High-Frequency Limit.- 4.1.5 Extension to All Frequencies.- 4.2 Extended Dynamical Theory.- 4.2.1 ?trap and Its Relation to a Soliton Model.- 4.2.2 Low-Frequency Conductivity.- 4.3 Applications to Silver Iodide and Hollandite.- 4.3.1 Silver Iodide: Structural Properties, Lattice Gas Representation.- 4.3.2 The Disorder Entropy of AgI.- 4.3.3 Dynami c Properties of ?-AgI.- 4.3.4 Collective Excitations in One-Dimensional Systems: Hollandite.- 4.4 Conclusions.- Appendix A.- Appendix B.- Appendix C.- References.- 5. Light Scattering in Superionic Conductors.- 5.1 Raman Scatteri ng.- 5.1.1 Silver Iodide.- 5.1.2 M+Ag4I5 (M+ = Rb+, K+, NH+4).- 5.1.3 Copper Halides.- 5.1.4 ?-Aluminas.- 5.1.5 Anion Conducting Fluorites.- 5.2 Low-Frequency Raman and Brillouin Scattering.- 5.2.1 Theoretical Considerations.- 5.2.2 Silver Halides.- 5.2.3 Other Superionic Conductors.- 5.3 Infrared Absorption and Frequency Dependent Conductivity.- 5.4 Conclusion.- References.- 6. Magnetic Resonance in Superionic Conductors.- 6.1 Theory of NMR Relaxation of and by Rapidly Diffusing Ions.- 6.1.1 General Correlation Functions and Interactions.- 6.1.2 Calculation of T1 and T2 from Correlation Functions.- 6.1.3 T1/T2 Ratio.- 6.1.4 Simple Random-Walk Values.- 6.1.5 Diffusion in Lower Dimensions.- 6.1.6 Effects of Correlated Hopping.- 6.2 Comparison with Experiment.- 6.2.1 Thermal Activation.- 6.2.2 Frequency Dependence.- 6.2.3 Prefactors.- 6.2.4 Coupling to Paramagnetic Impurities.- 6.3 Electron Paramagnetic Resonance.- 6.4 Structure Determination.- 6.5 Summary and Conclusions.- References.- 7. Phase Transitions in Ionic Conductors.- 7.1 Modern Theory of Phase Transitions.- 7.1.1 Landau Criteria.- 7.1.2 Renormalization Group.- 7.2 Models for Critical Behavior in Superionic Conductors.- 7.2.1 Quasi-Chemical Models.- 7.2.2 Lattice Gas Models.- 7.2.3 The Order Parameter for RbAg4I5.- 7.3 Critical Behavior of Physical Properties.- 7.3.1 Specific Heat.- 7.3.2 Ionic Conductivity.- 7.3.3 Acoustic Properties.- 7.3.4 Other Properties.- 7.4 Conclusions.- References.- 8. Continuous Stochastic Models.- 8.1 Models for Superionic Conductors.- 8.1.1 The Hamiltonian.- 8.1.2 Comparison of the Models from Microscopic Considerations.- 8.1.3 Correlation Functions.- 8.2 Continuous Models.- 8.2.1 Langevin Equation.- 8.2.2 Fokker-Planck Equation and Liouvillian.- 8.2.3 Continued-Fraction Expansion.- 8.2.4 Static Mobility, Diffusion Constant, dc Conductivity.- 8.2.5 Dynamic Mobility, ac Conductivity.- 8.2.6 Approximate Solutions and Similar Models.- 8.2.7 Dynamic Structure Factor for Jump Diffusion.- 8.2.8 Dynamic Structure Factor for Large Friction.- 8.2.9 Dynamic Structure Factor for General Friction.- 8.2.10 Light Scattering: Continuous and Continuum Models.- 8.2.11 Microscopic Foundation.- 8.3 Computer Simulations.- 8.4 Correlations Among the Mobile Ions.- References.- Additional References with Titles.

The Effect of Dispersed Alumina Particles on the Electrical Conductivity of Cuprous Chloride

Abstract: The electrical conductivity of cuprous chloride containing a dispersion of fine alumina particles was studied as a function of volume fraction (0–0.212) and particle size (0.3 and 0.06 μm initial particle size). At low temperatures the ionic conductivity may be increased by as much as two orders of magnitude. The enhanced conductivity, Δσ, was proportional to the surface area of the added alumina. Both these data and the earlier data of Liang (1) were fitted to a relation, where is the radius of the alumina dispersoids and the volume fraction.

Fast Ionic Transport in Solids

Abstract: The discovery of inorganic solids with ionic conductivities comparable to those of aqueous electrolytes has revolutionized solid-state electrochemistry. Sodium beta alumina, a Na+ conductor, and LixTiS2, an intercalation compound with simultaneous Li+ and electronic conductivity, are two of the best and most versatile fast ionic conductors. A wide variety of cations can replace Na+ in beta alumina and Li+ in LixTiS2 and change the properties of the materials. Sodium beta alumina and LixTiS2 are currently used in the development of high-energy density batteries for electric vehicles and electrical utility load leveling. Current research in solid ionic conductors is exploring new intercalation compounds, solid polymer electrolytes, and alkali ion and proton transport in crystalline solids.

Solid Electrolyte Behavior of NaMgF3: Geophysical Implications

Abstract: In the solid state, NaMgF(3) transforms smoothly with temperature into a solid electrolyte phase; the conductivity is 130 siemens per meter just below the melting point. The isostructural compound MgSiO(3) should behave similarly under conditions obtaining in the earth's lower mantle, and so it is expected that the electrical conductivity in that region is ionic rather than electronic.

The Ionic Conductivity of Fluorite‐Structured Solid Solutions of Composition: MF 2 : UF 4 : CeF3 ( M = Ca , Sr , Ba )

Abstract: The ionic conductivity of single crystals of the fluorite‐structured solid solutions where constitutes the predominant dopant has been studied as a function of temperature in the region 300°–550°K. The ionic conductivity of these solid solutions increases superlinearly upon doping, while simultaneously the conductivity activation enthalpy decreases. These results are in line with literature data on fluoride‐conducting solid solutions based on and with trivalent cation dopants. The increase of the conductivity in all these solid solutions is accounted for by an increase of the mobility of the mobile species due to interactions with defect clusters which are present in this concentration regime. It is shown that lattice relaxations in close proximity to the clusters lead to a distribution of activation enthalpies for fluoride‐ion motion via the interstitialcy mechanism. The shape of the distribution function and its dependence on the dopant concentration has been estimated on the basis of a simple model. The results are in line with the experimental data. In addition it is shown that the fluorite lattice with defect clusters can accommodate some maximum number of mobile interstitial fluoride ions.

Conductivity and creep in acceptor-dominated polycrystalline Al2O3

Abstract: Ionic and electronic conductivity and compressive creep of hot-pressed polycrystalline acceptor-dominated Al2O3 were measured as a function of oxygen partial pressure and grain size varying from 3 to 200 μm. Hole conduction shows a slight preference for grainboundaries; ionic conduction is slightly hindered by grain boundaries, indicating that fast oxygen grain-boundary diffusion involving charged species does not occur. Conductivity and creep are accounted for on the basis of a model in which there is fast grain-boundary migration by a neutral oxygen species.

Ag3SBr and Ag3SI: Ionic Conductivity of Their Modifications in the T Range 93—573 K

Abstract: Ag3SBr and Ag3SI obtained through a modified preparation procedure have been investigated in the temperature range 93 —573 by means of conductivity, DTA and X-ray diffraction determinations. At the phase transition temperatures the Arrhenius plot of the conductivity shows evident discontinuities, whereas in the range where Ag3SBr and Ag3SI have an antiperovskitic structure this plot shows an upward curvature: for Ag3SBr a reproducible \"knee\" is also observed. The recently recognized [9] low modifications of these compounds are poorly conducting. The general behaviour of the conductivity in the wide investigated range suggests a direct comparison between these salts and RbAg4I5 which shows analogous phase transitions and discontinuities in the Arrhenius plot of the conductivity. Electronic conductivity determinations confirm that the charge transport is predominantly ionic in either compound.

Superionic Conducting Oxides

Abstract: Fast ionic conduction in the solid state has been observed since the time of Faraday himself (1). Recently the increasing demand for new power sources and energy storage and conversion systems has led to a consider­ able interest in the field of solid electrolytes. Fuel cells and batteries are important devices in this respect. Solid superionic conducting materials have been extensively investi­ gated both for fundamental and technological aspects. Recent review books and papers (2-16) provide a comprehensive survey in that field. The present paper is limited to oxide compounds; special attention is paid to the latest results with emphasis on the relations between basic properties and observed fast ion conduction. Superionic conductors (SIC) are defined as materials with unusually high ionic conduction (0' > 10 2 n 1 em 1). Such values are normally found in molten salts, but some materials exhibit similar conductivity far below their melting point and even at room temperature. Their con­ ductivity may be purely ionic; the possible electronic contribution is several orders of magnitude lower. This property is required for solid electrolytes used in batteries, because excessive electronic conductivity will result in discharge of the system. Other compounds show mixed conductivity with high values for both ionic and electronic conduction, and they have useful applications mainly as electrodes in fuel cells or .batteries .

Mixed Conduction in AgCuSe

Abstract: Ag 1-δ CuSe is a mixed conductor, in which Ag + and Cu + ions, electrons, and holes are mobile. It transforms from the β phase to the α phase (superionic phase) at 200°C and melts at 780°C. The electronic and ionic properties in these three phases are studied with the help of the galvanic cell Ag|AgI|Specimen|Pt in the range of the temperature 100∼1000°C and of the composition δ=0∼1%.

A high‐pressure conductivity and laser Raman spectroscopic study of aqueous orthophosphate solutions at 25 °C

Abstract: Conductivities of aqueous solutions of H3PO4, KH2PO4, and Na3PO4 (0.001–1 M), and Raman spectra of 0.1, 0.5, 10, and 15.5 M H3PO4, 1 M KH2PO4, and 0.1M Na3PO4, have been obtained at 25 °C, and pressures up to 200 MPa. Pressure enhanced the first dissociation of H3PO4 (κp/κ⊥, measured by conductivity vs [H3PO4] goes through a maximum), and reduced the extent of hydrolysis of Na3PO4. Volume changes for the first and third dissociations of H3PO4 were ΔV1=21±4 cm3 mol−1 (conductivity), −18±3 (Raman, 0.1 M H3PO4), −8±2 (Raman, 0.5 M H3PO4), and ΔV3=−36±3 (Raman, 0.1 M Na3PO4). Both Raman and conductivity studies of H2PO4− were consistent with the presence of hydrogen‐bonded phosphate dimers, H4P2O82−, with a formation constant of 2–3 l mol−1 (conductivity), and ΔV?0 cm3 mol−1 (conductivity). This ΔV value agreed with the Raman study which indicated only a very small decrease in dimerization with increasing pressure.