Journal
SOLID STATE IONICS
Volume 130, Issue 1-2, Pages 71-80Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0167-2738(99)00309-4
Keywords
Brown millerite structure; oxygen deficient strontium cobaltite; ceramic membranes
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Atomic resolution Z-contrast imaging and electron energy-loss spectroscopy (EELS) were used to study the defect structure of oxygen deficient strontium cobaltite (SrCoO3-delta) after repeated oxidation/reduction cycles at elevated temperatures. Ordered microdomains were found in the reduced sample. Z-contrast imaging showed ordering in alternate CoO2 planes, characteristic for a brownmillerite-type vacancy ordered structure. EELS showed that the average valence state of cobalt had decreased after testing. In the tested sample, cobalt was found in + 3 and + 2 valence states, respectively. In addition, cobalt oxide precipitates were found at grain boundaries and in triple pockets in this sample, indicating a cobalt deficiency of the grains. The mechanisms for the formation of the observed microstructure are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.
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