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  • 1
    Electronic Resource
    Electronic Resource
    Production of tartrate and glycolate from the electrochemical reduction of glyoxylate (1994)
    Springer
    Journal of applied electrochemistry 24 (1994), S. 271-273 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00242896
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  • 2
    Electronic Resource
    Electronic Resource
    Ca12Al14O33 — A possible high-temperature moisture sensor (1989)
    Springer
    Journal of applied electrochemistry 19 (1989), S. 410-412 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract C12Al14O33 is a high temperature oxide ion conductor whose conductivity is very sensitive to the presence of water vapour for temperatures in the range ∼ 1000 to 1200° C. The changes are reversible and the conductivity may be recovered by heating in a dry atmosphere. Applications in an amperometric device are envisaged.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01015244
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  • 3
    Electronic Resource
    Electronic Resource
    Optimization of superconducting critical temperatures by control of cation and anion stoichiometry in Bi2Sr2CaCu2Oδ-based solid solutions (1995)
    Springer
    Journal of materials science 30 (1995), S. 2743-2746 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract T c data are reported for powders of cation-stoichiometric Bi2Sr2CaCu2Oδ and for nonstoichiometric samples based on the three mechanisms Bi⇄Sr, Sr⇄Ca and Sr vacancy. For each, the T c values depend critically on the final oxygen contents, which were varied by heating samples in either O2 or N2 at different temperatures. Stoichiometric Bi2Sr2CaCu2Oδ has the highest T c, 92 K, obtained after heating in O2 at ∼ 820 °C. Heating in O2 at lower temperatures gives rise to overdoping and T c decreases to 60 K. The other cation compositions show a smaller maximum T c but also less reduction in T c on overdoping. Under-doped samples, with reduced T c values were obtained on heating in N2. These data, together with selected literature results, lead to a unified picture of the variation of T c with cation composition and oxygen content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00349639
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  • 4
    Electronic Resource
    Electronic Resource
    Sinterability of commercial 8 mol% yttria-stabilized zirconia powders and the effect of sintered density on the ionic conductivity (1998)
    Springer
    Journal of materials science 33 (1998), S. 4297-4305 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The sintering behaviour of a number of commercially produced 8 mol% yttria-stabilized zirconia powders has been studied. The effect of different sintering regimes on the density and microstructure of the sintered ceramic was determined using density measurements, scanning electron microscopy (SEM) and dilatometry. The chemical homogeneity, particle size and the morphology of the as-received powder were related to the sintering behaviour of the different commercial powders. Powders prepared via a route which involved a spray-drying step sintered more readily than those prepared without a spray-drying step. Plasma-derived powders did not sinter to as high an apparent density as co-precipitated powders. The effect of sample density on the ionic conductivity of sintered YSZ ceramics was studied using a.c. impedance spectroscopy. This technique allowed separation of the bulk and grain-boundary components, enabling clear intepretation of the effects of sample porosity of the conduction pathways. Ceramics prepared from the three different powders achieved a bulk ionic conductivity of ∼16 S cm-1 at 1000 °C for sintered densities of 95% or greater. The results obtained are compared to values reported for a variety of other commercial powders. © 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004435504482
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  • 5
    Electronic Resource
    Electronic Resource
    High oxide ion conductivity in non-stoichiometric pyrochlores and fluorites in the ternary system ZrO2 - Gd2O3 - TiO2 (1997)
    Springer
    Ionics 3 (1997), S. 30-35 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The extents of the cubic fluorite and pyrochlore regions in the ternary oxide system ZrO2-Gd2O3-TiO2 have been determined experimentally. AC impedance measurements of single phase fluorite and pyrochlore compositions show high oxide ion conduction in compositions containing 20 mol% TiO2. Resolution of the bulk and grain boundary contributions to the total conductivity show that the bulk ionic conductivity increases with Gd2O3 content up to the stoichiometric composition containing 33.33 mol% Gd2O3 and then decreases upon further addition of the aliovalent dopant. Trends in conductivity as a function of temperature and dopant density are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375521
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical characterization of highly Titania doped YSZ (1998)
    Springer
    Ionics 4 (1998), S. 215-219 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The defect fluorite region of the ternary system ZrO2-Y2O3-TiO2 encompasses compositions which offer both, good electronic and oxygen ion conductivity which enable good catalytic activity for the direct oxidation of methane in a solid oxide fuel cell (SOFC). The electrical properties of compositions YxTiyZr1−(x+y)O2−x/2 (with x=0.15, 0.2, 0.25 and y=0.15, 0.18) were characterised in order to find the composition with highest ionic and electronic conductivity. High titanium dopant concentrations (Y) of 15 and 18 atom%, near the solubility limit of Ti4+ in the fluorite structure, have been introduced to achieve a high electronic conductivity at low oxygen partial pressure. The yttrium content x has been varied between 15 and 25 atom% to find the fluorite composition with the highest ionic conductivity for each titanium level. In the pO2-range from 0.21 to 10−13 atm the conductivity is predominantly ionic and constant over that range. The maximum ionic conductivity is 0.01 Scm−1 for the compositions, which contain 15 atom% yttrium. Substantial electronic conductivity is introduced into the system at low oxygen pressures below 10−13 atm via reduction of Ti4+ ions to Ti3+. The maximum electronic conductivity of 0.2 Scm−1 at 930 °C has been measured for a sample with 18 atom% titanium. The slope of all log(σ) vs. log(pO2) plots follows a pO 2 −1/4 -dependence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375948
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  • 7
    Electronic Resource
    Electronic Resource
    The optimisation of mixed conduction in potential S.O.F.C. anode materials (1998)
    Springer
    Ionics 4 (1998), S. 61-71 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The success of the SOFC rests heavily on materials selection. In this work we address the optimisation of mixed conductivity in fluorite compounds in the search for new improved SOFC anodes based upon oxides. The mobility of electronic carriers is considered to be much higher than that of ionic defects, therefore, doping a good ionic conductor with a small concentration of reducible transition metal ions can form promising mixed conductors. Zirconia based mixed conductors were studied for two reasons. Firstly, zirconia, stabilised in the defect fluorite structure, exhibits a high level of ionic conductivity. Secondly it is the most common electrolyte material for a S.O.F.C. An anode based on zirconia would therefore be expected to offer a good physical compatibility with the electrolyte material and to exhibit a high ionic contribution to total conductivity. Work on the system ZrO2-Nb2O5-Y2O3 showed that the influence of composition on conduction could be determined. This enabled the optimisation of both the electronic and ionic contributions to conduction by compositional selection. These factors were extended to explain conductivity behaviour observed in the comparable system ZrO2-TiO2-Y2O3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02375781
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  • 8
    Electronic Resource
    Electronic Resource
    Oxide ion transport in highly defective cubic stabilized zirconias (1995)
    Springer
    Ionics 1 (1995), S. 279-285 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ac impedance spectroscopy and neutron powder diffraction have been used to study the high temperature behaviour of defective fluorite solid electrolytes. In yttria-stabilised zirconia with an yttrium content of 15 mol% YO1.5 there is a marked change in conductivity behaviour at around 650 °C, with a decrease in activation energy of 0.15 eV. Structural studies confirm that this is due to a change in the bulk of the sample with the disappearance of diffuse scattering peaks and marked changes in the behaviour of the isotropic temperature factors at the same temperature. These results indicate that the change in activation energy of yttria-stabilised zirconia at 650 °C is due to an order-disorder transition involving local defect clusters. In studies of zirconia co-doped with yttrium and niobium, activation energy for conduction is found to rapidly increase with the concentration of the trivalent yttrium Saturation doping is reached at about 20–30 % of yttrium and activation energy only increases slightly with doping. Introduction of pentavalent niobium at this level of doping serves to decrease activation energy, although it also decreases conductivity slightly. The low and high temperature activation energies converge as the saturation regime is approached. These observations seem to suggest that ordering of defect clusters into microdomains increases activation energy for ionic motion. At low defect concentrations and high temperatures, this local ordering breaks down and the activation energy for conduction decreases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02390208
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and electrical characterisation of the perovskite niobate-titanates, Sr1−x/2Ti1−xNbxO3−δ (1996)
    Springer
    Ionics 2 (1996), S. 213-216 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The synthesis and electrical characterisation over a range of oxygen partial pressures (10−20 to 1 atm) are reported for the cubic perovskite niobate-titanates Sr1−x/2Ti1−xNbxO3−δ, which are proposed as potential anode materials for solid oxide fuel cells. Single phase samples were observed for 0≤x≤0.4, and phase purity was retained on annealing at both high and low oxygen partial pressures. Good electrical conductivity was observed on reduction in low oxygen partial pressures, with a maximum for the sample with 25% Nb (x=0.25), σ=5.6 Scm−1 at 930°C (P (O2)=10−18 atm). For dense samples the higher the Nb content the more resistant the reduced sample was to reoxidation as the oxygen partial pressure was increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02376024
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis and ionic conduction of apatite-type materials (2000)
    Springer
    Ionics 6 (2000), S. 389-396 
    Details
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Apatite is a mineral with general formula M10(XO4)6Z2, where M are metallic elements such as Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Ln3+ etc.; X=P, V, S, Si, Ge, Re, Cr etc; Z=F−, Cl−, I−, OH−, O2−, S2− etc. Some materials with apatite structure (S.G. P63/m) exhibit quite high cationic (Li+, H+ etc.) and/or anionic (F−, Cl− etc.) conduction. Recently, it was reported that some rare earth silicates, e.g., La10(SiO4)6O3, exhibit quite high oxide-ion conductivity. In this paper, we discuss chemical composition, structure, synthetic procedure and ionic conduction of apatite-type materials. Recent improvements are briefly reviewed. High ionic conductivity has been observed for both cation deficient, oxygen stoichiometric La9.33(SiO4)6O2 and cation stoichiometric, oxygen excess La10(SiO4)6O3 compositions. Grain boundary conductivity is usually low, which tends to dominate the impedance response. The resistance, particularly the grain boundary resistance is also found to depend on pO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02374158
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