Characterization of La{sub 0.8}Sr{sub 0.2}FeO{sub 3-{delta}} and La{sub 0.7}Sr{sub 0.2}FeO{sub 3-{delta}} as a function of temperature by x-ray absorption spectroscopy
- Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 (United States)
A temperature-dependent x-ray absorption spectroscopy (XAS) study was performed to investigate the changes in electronic and atomic structure of La-deficient La{sub 0.7}Sr{sub 0.2}FeO{sub 3-{delta}} (L7S2FO3) and stoichiometric La{sub 0.8}Sr{sub 0.2}FeO{sub 3-{delta}} (L8S2FO3). La{sub 0.8}Sr{sub 0.2}FeO{sub 3-{delta}} is a promising cathode material for intermediate operating temperature (700-800 deg. C) solid oxide fuel cells. Performance improvements have been shown by increasing the La- or A-site deficiency in this material but a clear understanding of the mechanisms responsible for this improvement are still needed. Here we report an x-ray absorption spectroscopy (XAS) study as a function of temperature to investigate electronic and atomic structure changes of La-deficient La{sub 0.7}Sr{sub 0.2}FeO{sub 3-{delta}} (L7S2FO3) and stoichiometric La{sub 0.8}Sr{sub 0.2}FeO{sub 3-{delta}} (L8S2FO3). In particular we have measured the temperature-dependent changes in oxidation state, bond distance, Fe coordination number, and oxygen vacancies for both compounds. L7S2FO3 contains 10% A-site vacancies compared to stoichiometric L8S2FO3, which has a fully occupied A site and thus some form of charge compensation is necessary in the former to maintain charge neutrality. X-ray absorption near edge spectroscopy shows the presence of Fe{sup 3+} and Fe{sup 4+} in both L7S2FO3 and L8S2FO3 (mixed valence) as established by comparison with model compounds. Studies from room temperature to 850 deg. C show that Fe{sup 3+} dominates over Fe{sup 4+} in both materials with increasing dominance as the temperature is increased. Furthermore, the temperature-dependent study revealed the La-deficiency in L7S2FO3 leads to a higher concentration of both electron holes (i.e., more Fe{sup 4+} created) and oxygen vacancies, compared to the stoichiometric L8S2FO3. Analysis of the extended x-ray absorption fine structure shows that the Fe-O bond increases with the increase in temperature for both the systems.
- OSTI ID:
- 20788001
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 73, Issue 11; Other Information: DOI: 10.1103/PhysRevB.73.115114; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
ABSORPTION SPECTROSCOPY
BOND LENGTHS
CATHODES
COMPARATIVE EVALUATIONS
COORDINATION NUMBER
FERRITES
FINE STRUCTURE
HOLES
IRON IONS
LANTHANUM COMPOUNDS
OXYGEN
PERFORMANCE
SOLID OXIDE FUEL CELLS
STOICHIOMETRY
STRONTIUM COMPOUNDS
TEMPERATURE DEPENDENCE
VACANCIES
VALENCE
X RADIATION
X-RAY SPECTROSCOPY