Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum cobaltite |
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| Institution: | 1. Fuel Cells and Solid State Chemistry Department, Risø National Laboratory, Frederiksborgvej 399, DK-4000 Roskilde, Denmark;2. Department of Chemistry, University of Southern Denmark-Odense University, DK-5230 Odense M, Denmark;1. University of St Andrews, School of Chemistry, KY16 9ST, St Andrews, United Kingdom;2. TOPSOE FUEL CELL A/S, Nymøllevej 66, DK ? 2800, Kgs. Lyngby, Denmark;3. Technical University of Denmark, Department of Energy Conversion and Storage, Frederiksborgvej 399, P.O. Box 49, Bygning 778, 4000 Roskilde, Denmark;1. Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK;2. Department of Materials, Imperial College London, SW7 2AZ, UK;1. Department of Physics, Manipal Institute of Technology, Manipal University, Manipal 576104, India;2. Microtron Centre, Department of Studies in Physics, Mangalore University, Mangalagangotri 74199, DK, Karnataka, India;3. UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452017, India;4. UGC-DAE Consortium for Scientific Research, R5 Shed, Bhabha Atomic Research Centre, Mumbai 400085, India;1. Karlsruhe Institute of Technology (KIT), Institut für Werkstoffe der Elektrotechnik (IWE), Adenauerring 20b, D-76131 Karlsruhe, Germany;2. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research (IEK-1), D-52425 Jülich, Germany;1. Department of Physics, University of Engineering and Technology, Lahore, 54890, Pakistan;2. Department of Chemical Engineering, College of Engineering, King Saud University, P.O BOX 800, Riyadh, 11421, Saudi Arabia;3. Clean Energy Research Lab (CERL), Department of Physics, COMSATS University Islamabad, Lahore Campus, Lahore, 54000, Pakistan;4. Department of Physics, University of Sahiwal, Sahiwal, Pakistan;5. Department of Physics, Chemistry and Biology, Semiconductor Materials, Linköping University, Sweden |
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| Abstract: | Oxygen nonstoichiometry, structure and transport properties of the two compositions (La0.6Sr0.4)0.99CoO3?δ (LSC40) and La0.85Sr0.15CoO3?δ (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, σ, of the materials is high (σ > 500 S cm? 1) in the measured temperature range (650–1000 °C) and oxygen partial pressure range (0.209–10? 4 atm). At 900 °C the electrical conductivity is 1365 and 1491 S cm? 1 in air for LSC40 and LSC15, respectively. A linear correlation between the electrical conductivity and the oxygen vacancy concentration was found for both samples. The mobility of the electron-holes was inversely proportional with the absolute temperature indicating a metallic type conductivity for LSC40. Using electrical conductivity relaxation the chemical diffusion coefficient of oxygen was determined. It was found that accurate values of the chemical diffusion coefficient could only be obtained using a sample with a porous surface coating. The porous surface coating increased the surface exchange reaction thereby unmasking the chemical diffusion coefficient. The ionic conductivity deduced from electrical conductivity relaxation was determined to be 0.45 S cm? 1 and 0.01 S cm? 1 at 1000 and 650 °C, respectively. The activation energy for the ionic conductivity at a constant vacancy concentration (δ = 0.125) was found to be 0.90 eV. |
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