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  • 1
    ISSN: 0167-2738
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Basic investigations on the electrochemical behavior of alumosilicate zeolites were conduced in gas atmosphere and aqueous solution using impedance spectroscopy under in situ conditions where “zeolitically” bound water molecules are present in the channel and cage system. Natural stilbite (STI) and heulandite (HEU), zeolites of structure types with the same 4 – 4 = 1 building units, were used for these investigations. At a given temperature, well defined water partial pressures were applied in the gas atmosphere (in situ conditions) and the effect of polar organic molecules on conductivity was investigated. Furthermore, the effect of complete water saturation of the channel system on the Arrhenius type activation energy of conductivity was investigated in aqueous solution in comparison. The ion-exchange behavior of zeolite materials could be monitored under these conditions. These results show that, dependent on the different parameters affecting the zeolite conductivity behavior, they are applicable in the field of electrochemical analysis if these basic results on single crystals are transferable to polycrystalline materials.
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  • 3
    ISSN: 1433-0768
    Keywords: Key words Lithium nickelate ; Solid state electrochemisty ; Proton intercalation ; Voltammetry ; Immobilized microparticles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lithium nickelate was synthesized by self-propagating high-temperature combustion. The electrochemical behaviour of the product was studied by cyclic voltammetry of microparticles immobilized on the surface of graphite electrodes. Whereas numerous previous studies have dealt with non-aqueous electrolyte solutions, here the behaviour of lithium nickelate in contact with aqueous electrolyte solutions was investigated. It could be shown that protons are intercalating upon reduction of the Ni(III) to Ni(II) and deintercalating upon oxidation. This insertion electrochemistry is chemically reversible. Within 1600 oxidation-reduction cycles, the response diminished only by about 10%. Scanning electron microscopy reveals a considerable recrystallization during the electrochemical cycles. Energy dispersive X-ray detection proved that no metal cations are intercalating. The electrochemical system is accessible only in very alkaline solutions as it shifts to more positive values with decreasing pH.
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  • 4
    ISSN: 0167-2738
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Solid State Ionics 68 (1994), S. 177-184 
    ISSN: 0167-2738
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Ionics 1 (1995), S. 106-111 
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Modified active electrode materials based upon rare earth manganites were developed for different solid electrolyte electrochemical cells. The preparation, structure, thermal expansion, the state of oxygen on the surface, the electronic and ionic conductivity of the perovskites Ln1−xCa(Sr)xMn1−y(Co, Ni)yO3−δ with various compositions and electrode kinetics on the manganite electrode/solid electrolyte interfaces were investigated. The value of the bulk conductivity was larger than 150 S/cm (at 1100 K) and increased significantly with increasing contents of Ni or Co. The thermal expansion coefficients of rare earth manganites were close to those of ZrO2 based solid electrolytes. The expansion coefficients of Co or Ni subsituted lanthanum manganites increase with Co or Ni substitution and are over 12•10−6K−1. The ionic conductivities were determined using encapsulated zirconia microelectrodes based on a Hebb-Wagner analysis of the currentvoltage curves. The relatively high oxide ion conductivity of 10−5 S/cm at 900...1000 K was found by Ni or Co doped manganites. Studies of the electrode kinetics using complex impedance spectroscopy show that Co and Ni doped manganites have advantages if used as electrodes as compared with these for noble metals.
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  • 7
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The conductivity behavior of the natural single crystal zeolites ANA, BRE, CHA, HEU, PHI and STI was investigated in the temperature range between 60 °C and 110 °C. The effect of combustible gas components on the conductivity was also investigated using constant water vapor pressure conditions. In the temperature range studied, the conductivity is assumed to be mainly ionic and zeolitic water remains within the channel and cage system of the structures. All zeolites do have different frameworks, channel systems, channel sizes, channel cations and water contents. Dependent on the zeolite type, water partial pressures and combustible gas components cause different effects on the conductivity which are correlated with the geometry, charge distribution and occupation of the channels and cages of the respective zeolite single crystal.
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  • 8
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Natural clays were characterized by XRD, TGA and SEM/EDX, then pressed to pellets and analyzed by impedance measurements under various defined gas compositions and temperatures. From the Nyquist plot, conductivity values were calculated for the different clay samples. A strong dependence of the conductivity on the water vapour concentration at low temperatures was found for all investigated clay samples. Partial substitution of water by methanol led to a decrease in conductivity at low temperatures, confirming the essential role water plays in the conductivity mechanism at these temperatures. Increasing the temperature resulted in a decrease in conductivity, until a turn-over point was reached. Beyond this temperature an Arrhenius behaviour was observed, suggesting a change in the conductivity mechanism.
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  • 9
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sensors with solid electrolytes provide the possibility of correct and fast measurements of partial pressures of various gases. By modification of the solid electrolyte, sensors with specific performances may be manufactured. Layers of Na+-, Li+-, Ca2+- and Sr2+-β“-alumina on top of polycrystalline α-alumina substrates were produced by an in-situ formation process and were used as solid electrolytes for CO2 and SOx sensors. Carbonates and sulphates were applied as measuring electrodes and oxidic mixtures of SiO2 and silicates were used as reference electrodes. The different performance of these sensors was investigated over a wide temperature range and the results were compared with theoretical data. Different solid electrolyte / electrode combinations were applied, which all showed different characteristic cross sensitivities against water and organic components.
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  • 10
    ISSN: 1862-0760
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Investigations on lanthanum gallium chromium mixed oxides of the compositions La1.0Ga0.2Cr0.8O3−d and La0.9Ga0.2Cr0.8O3-d are presented regarding their structure, redox stability, conductivity and catalytic activity for the oxidation of propene. The mixed oxide has perovskite-type structure, high redox stability, an electronic p-type conductivity and low catalytic activity. If the perovskite-type compound has a deficiency of lanthanum, the electronic conductivity, surface area and catalytic activity are significantly higher. The catalytic activity is likely comparable to that of gold. Similar to gold electrodes of solid electrolytes, oxygen electrodes formed with gallium doped lanthanum chromite show a relatively high sensitivity to hydrocarbons such as propene at temperatures of about 700 °C. The mixed oxide is possibly suitable as electrode material for exhaust gas sensors using oxide-ion conducting solid electrolytes.
    Type of Medium: Electronic Resource
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