LiV308 powder has been prepared on a large scale by spray drying ofan aqueous gel. The material was further dehydrated at 150 and 350ºC. These materials were characterized by TGA, XRD and electrochemical methods. Materials dried at 150 and 350ºC, showed an unusual high reversible capacity, close to 4 Li per formula unit, and cycle well. The material dried at 350ºC is very similar to the crystalline LiV308 prepared by conventional high temperature synthesis.

The high redox potential and ion insertion properties of vanadium pentoxide have made this material a viable cathode for secondary lithium batteries. The use of sol-gel methods to synthesize vanadium pentoxide and other transition metal oxides has been well studied as the technique represents a relatively simple approach for preparing thin films and powders. Although it is well known that sol-gel processing may be used to prepare high surface area aerogels, the research on transition metal oxides has been largely limited to xerogels. The present paper compares the properties, structures and morphologies of vanadate xerogels and aerogels.

A lattice-gas model is presented, where ions are diffusing in an energy landscape due to immobile, randomly placed counterions. All Coulombic interactions are taken into account.By Monte Carlo simulations we obtain the ac-conductivity, which shows strong dispersion in the form of power-laws. In a separate study we investigate a restricted model, where long-range diffusion is suppressed. These calculations suggest that the response at high frequencies can be interpreted in terms of highly correlated, local motions of dipolar character. Conductivity exponents n1 near unity or even exceeding unity arefound in that regime. We discuss the relationship of these results to experiments on ionic transport in alkali-doped network glasses.

Complete conductivity spectra have been taken of a lithium ion conducting glass of composition B2O3 · 0.56Li2O · 0.45LiBr and of lithium stabilized Na-β″-alumina, at various temperatures. — In the glass, it has forthe first time been possible to separate the hopping and vibrational contributions to theconductivity. The resulting hopping conductivity spectra display high-frequency plateaux similar to those known to exist in crystalline solid electrolytes like RbAg415 and Na-β-alumina. In the dispersive regime, the spectra are characterized bytwo different power-law exponents, p = 0.6 and q = 1.3. The data are evaluated by combined application of the jump relaxation model and the dynamic structure model. — Na-β″-alumina has pronounced high-frequency plateaux between about 200 GHz and 400 GHz. The hopping observed in the spectra can be decomposed into hops that are a priori unsuccessful and others that can be treated in terms of the jump relaxation model. The latter fraction is found to increase with increasing temperature.

The progress of dynamically disordered hopping (DDH) in modelling charge transport in polymer electrolytes is reviewed. The DDH model successfully describes many of the salient features of polymer electrolytes, most notably, the frequency and temperature dependence of the conductivity. Furthermore, analyses and simulations based on the DDH model provide rich mechanistic information. The general picture of charge transport that emerges from the DDH model is one in which two classes of charge carriers exist in thermal equilibrium:quasi-free and bound. The quasi-free carriers dominate the conductivity response and diffuse freely over short distances (≈1Å) with longer range diffusion requiringlocal segmental motions, renewal in the language of DDH, of the polymer solvent. The bound carriers, which are likely polymer solvated ion clusters, are immobile on the time-scale of renewal and contribute relatively little to the conductivity.

Results of the theoretical study of the effects produced on ionic crystals by highfrequency electric fields of moderate intensity are presented. The ponderomotive action of the electric field on the space charge induced by it in a thin layer within the crystal near its surface causes directional mass transport that leads to plastic deformation and induces a stationary distribution of electric potential. The analysis shows that the proposed effect (that appears to be equivalent to the action of mechanical stresses which exceed the electromagnetic pressure by many orders of magnitude) can influence the results of processing of ionic crystalline materials significantly.

Defect chemical models have been found to be useful in establishing defect generation andtransport mechanisms, extracting thermodynamic data and deconvoluting contributions to the total electrical conductivity. In most cases, however, the utility of the approach has been limited due to the imposed simplifications made to make the analysis more tractable, e.g. the simplified neutrality relation and the elimination of defect associates. In thiswork, we treat more complex equilibria with the aid of numerical methods and illustrate how this approach can be used, not only to extractkey thermodynamic and kinetic data, but also to assist in the design and optimization of materials. Some specific examples with application to solid state ionics will be used to illustrate this approach.

We have investigated the defect structure and protonic transport properties of nonstoichiometric complex perovskite-type compounds of the type A3B'1+xNb2-xO9-δ. where A and B' are both divalent ions. Protons are incorporated by treatment in H2O vapor and their presence is manifested by the appearance of an OH band in the IR spectra, as well as by the large increase in electrical conductivity to produce excellent protonic conductors, with lower activation energies. A non-classical isotope effect, in which the Arrhenius plots for D+ and H+ cross over, can be explained by a modification of the classical ART hopping theory.

The high fluoride ion conductivity of fluorite type MF2 has been attributed tothe fact that half of the F8 cubes present in this structure are empty and therefore, are potential vacant sites for interstitial fluoride ions in the formation of Frenkel defects. However, the model of long range ion motion through Frenkel defects by use of empty F8 cubes is in contradiction with: (i) the little difference between the conductivities of CaF2 and BaF2, (ii) the conductivity of β-PbF2 being much larger than that of BaF2, and (iii) the much higher performance of MSnF4 even though there is no empty cube to form Frenkel defects in the MSnF4 structures.

The deviation from stoichiometry, δ, in Co1-δ O was measured in-situ as a function of oxygen activity at temperatures between 1000 and 1400 ºC, using ahigh resolution microbalance. The experiments were conducted over the entire Co1-δO phase stability region at atmospheric pressure. The experimental results were analyzed with regard to the point defect structure and also in comparison with mass and charge transport data. Contrary to prior belief, it was found that the average mobility of the cationic defects and holes varied with their respective concentration.

Cation diffusion in the spinel solid solution (Fe1-xTix)3-δO4 (0≤ x ≤ 0.3) was investigated at 1200 ºC as a function of oxygen activity, aO2 and cationic composition, x. At different cationic compositions, cation tracer diffusion coefficients, D*Me of Me = Fe and Ti were measured as a function of oxygen activity. Plots of log DMe vs. loga0 show V-shaped curves, indicating that different types of point defects prevail at high anc low oxygen activities. Thermogravimetric experiments were conducted, using a high resolution microbalance, to determine the deviation from stoichiometry in (Fe1-xTix)3-δO4 at 1200 °C. δversus log aO2 curves are S-shaped. An analysis of the oxygen activity dependences of thecation diffusion coefficients and the deviation from stoichiometry with regardto the point defect structure suggests that at high oxygen activities cation vacancies are the predominant defects governing the deviation from stoichiometry and the diffusion ofcations. At low oxygen activities, and at small values of x, cation interstitials determine the deviation from stoichiometry, while they dominate for 0 ≤ x ≤ 0.3 inthe cation diffusion.

A thermogravimetric study was conducted on synthetic olivines (FexMg1-x)2SiO4' prepared either by a conventional ceramic methodor a sol-gel method, to determine the nonstoichiometry and the point defect structure. Measurements were carried out as a function of oxygen activity and cationic composition at elevated temperatures. To avoid the dissolution of transition metal components of the silicate into noble metal containers, commonly used in previous investigations, quartz containers were used. The analysis of the point defect structure of olivines based on the new experimental results is presented.

The cation diffusion in the spinel solid solution (CrxFe1-x)3-δO4 (0 ≤ x ≤ 0.5) was experimentally investigated at 1200 °C as a function of oxygen activity, aO2 (= PO2/P°with P° = 1 bar) and cationic composition, x. Cation tracer diffusion coefficients, DMe' of Me = Co, Cr, Fe and Mn, were determined using the radioactiveisotopes Co-60, Cr-51, Fe-59 and Mn-54. For each cationic composition V-shaped log DMe vs. log aO2 plots were obtained. The observed oxygen activity dependences indicate that the cation diffusion is determined by different point defect species prevailing at high and low oxygen activities, respectively. The observed oxygen activity dependences, in comparison with considerations based on point defect thermodynamics, suggest that cations diffuse via cation vacancies at high aO2' while at low aO2 cation interstitials prevail in the cation diffusion. In addition, new experimental data for tihe deviation from stoichiometry ≤in (CrxFe1-x)3-≤O4 are presented and discussed.

Lead fluoride is a superionic conductor with the fluorite structure. Results of the measurement of linear thermal expansion of lead fluoride (reported earlier in literature) showed a large increase in the thermal expansion coefficient near 700 K where the ionic conductivity has been shown to exhibit a sharp increase. It is believed that thermally-generated defects in a crystal lattice affect the thermal expansion coefficient. This idea was applied in the present analysis to calculate the defect formation energy (Ef) by using the literature values of the coefficient of thermal expansion. It was assumed that the thermal expansion in excess of that produced due to the lattice anharmonicity (δ∝) is proportional to the concentration of defects (n). With this assumption, one may write: δ∝ = c nº exp(-Ef/kT), where c is a constant. For lead fluoride, a plot of ln(δ∝) versus (l/T) yielded Ef = 0.56 eV which is lower than the literature values. The assumptions in this analysis and the discrepancy in the result are discussed.

Systematic experiments on anion-deficient ABO3-δ perovskites are reviewed with a view to the development of a strategy for the design of improved oxide-ion electrolytes. Ba0.6 La0.4 1nO2.7 is shown to be competitive with the best yttria-stabilized zirconia and La0.9 Sr0.1 Ga0.8Mg0.202.85 to be a superior oxide-ion electrolyte suitable for fuel-cell applications.

Substitution of Nb, Ti, or Sn for In and of La for Ba was used to obtain cubic, anion-deficient perovskites AB03-δ. Neither the ferroelectric character of Nb5+ and Ti4+, nor the more acidic character of Sn4+ suppressed water absorption into the anion vacancies at temperatures T < 500ºC. However, the smaller La3+ ion in Bal-xLaxO2.5+0.5x did suppress the absorption of water for x = 0.4, and Ba0.6La0.4InO2.7 is competitive with yttria-stabilized zirconia as an oxide-ion electrolyte.

Research into the growth of high-quality single crystal thin films of high transition temperature (Tc) superconductors have stimulated interest in other perovskite metal oxides with a variety of physical properties.1 Thin films of perovskite materials are among the major focal research areas for optical, sensor, electronic, and superconducting applications.1 Two lanthanumbased oxygen/electronic conducting perovskite oxides of particular interest for high temperature fuel cell electrodes and interconnects and for other electrochemical applications such as oxygen separation devices are Lal-xSrxMnO3-y and Lal-xSrxCoO3-y. The La-based perovskites are valuable for these technologies because they reduce interfacial resistances by eliminating the need for a three phase contact area (gas, metal electrode, electrolyte).2 In addition, these oxides may also serve a valuable role as novel catalysts or catalytic supports; however, little is known about what catalytic properties they may possess.

Oxygen-deficient layered bismuth oxides, Bi2Sr2M'2M”O11.5 [(M' = Nb, Ta) and (M” = Al, Ga)] were synthesized. Powder X-ray diffraction and transmission electron microscopy were usedto characterize the new materials' structures. The ionic conductivity was measuredusing impedance spectroscopy which indicated the existence of multiple conductive states in the new oxygen-deficient materials. Arrhenius plots of the conductivity showed discontinuities which were attributed to transitions between different conductive states. At 800ºC, Bi2Sr2Nb2GaO11.5 and Bi2Sr2Nb2A1O1.5, have ionic conductivities of 2.0×10−2 S/cm and 1.2×10−2 S/cm, respectively. Differential thermal analysis showed phase transitions in the oxygen-deficient materials. These transitionsoccurred at temperatures similar to those at which discontinuities were observed in the Arrhenius plots of the conductivity and are attributed to oxygen vacancy order/disorder transitions. The transference number was calculated for some of the samples by measuring both the EMF and the conductivity as a function of oxygen partial pressure. Under atmospheric conditions the new materials are predominantly ionic conductors.

The ac electrical conductivity versus temperature dependence of solids undergoing phase transitions incorporating various guest ions, viz isovalent cations and anions, ions with different ionic radius, ions with different polarizability, in Na2SO4-based, Ag2SO4-based, Li2SO4-based and U02SO4-based compositions along with MxTl(1x)I compositions for 1 ≤ x ≤ 0.13, whose M = K, Rb, Cs, are reported. An overview is given of the interplay of various factors, structural and non-structural, with their contribution limits impacting on locking-in the fast cation conductivity phase and the interpretation of fast-ion conductivity in the context of a percolation-type of ionstransport mechanism.

Electrical conductivity measurements were performed on Gd2Sn207 as a function of temperature, P02 and Ca doping concentration. An effective frenkel constant and oxygen vacancy mobility were derived. The high level of intrinsic anion disorder found in this study is consistent with expectations based on the cation radius ratio (rA/rB) which was earlier found to be important in determining anion disorder in A2B207 pyrochlore compounds [1]. The magnitude of the ionic conductivity in Gd2Sn2O7 was found to be depressed relative to Gd2(Til-xZrx)207 based systems due to a high oxygen vacancy migration energy.