Oxygen incorporation in porous thin films of strontium doped lanthanum ferrite

Martin Søgaard, A. Bieberle-Hütter, Peter Vang Hendriksen, Mogens Bjerg Mogensen, H.L. Tuller

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Electrical conductivity relaxation measurements were carried out on thin films of (La0.6Sr0.4)0.99 FeO3 − δ deposited on MgO (100) substrates by pulsed laser deposition in order to determine the surface exchange coefficient, k Ex, of the oxygen incorporation process in the temperature range 550–700°C. The composition of the films was verified using wavelength dispersive x-ray and Rutherford backscattering spectroscopy. Scanning electron microscopy showed small triangular crystallites with the largest dimension 80 nm and the smallest dimension 10 nm. X-ray diffraction showed a cubic perovskite structure and significant texturing. At a constant temperature, k Ex was found to be a function only of the final pO2pO2 of the pO2pO2-changes the sample was subjected to during conductivity relaxation experiments, confirming that the magnitude of the exchange coefficient was not influenced by changes in ionic defect concentrations. The k Ex-values determined for these thin films were significantly lower than for bulk samples. A value of 3.6 × 10 − 6 cm s − 1 was obtained at 702°C and a final pO2pO2 of 0.048 atm, approximately a factor of six lower than that obtained for bulk samples. An activation energy of 282 ± 20 kJ mol − 1 was found for the surface exchange coefficient at pO2pO2 = 0.048 atm. Possible reasons for the reduced magnitude of k Ex are discussed including the role of thermal history in influencing surface morphology and chemistry.
    Original languageEnglish
    JournalJournal of Electroceramics
    Volume27
    Issue number3-4
    Pages (from-to)134-142
    ISSN1385-3449
    DOIs
    Publication statusPublished - 2011

    Keywords

    • Solid Oxide Fuel Cells
    • Impedance
    • Sensors
    • Materials
    • ELECTRICAL-CONDUCTIVITY RELAXATION
    • Conductivity relaxation
    • REDUCTION KINETICS
    • Oxygen reduction kinetics
    • Transport-properties
    • Stability
    • CHROMITES
    • CHEMICAL DIFFUSION-COEFFICIENT
    • Electrodes
    • Thin film
    • Deposition
    • LSF
    • NONSTOICHIOMETRY

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