Characterization of La0.8Sr0.2FeO3-δ and La0.7Sr0.2FeO3-δ as a function of temperature by x-ray absorption spectroscopy

被引:19
作者
Deb, A
Ralph, JM
Cairns, EJ
Bergmann, U
机构
[1] Univ Calif Berkeley, Lawrence Berkeley Lab, Environm Energy Technol Div, Berkeley, CA 94720 USA
[2] Argonne Natl Lab, Div Chem Engn, Argonne, IL 60439 USA
[3] Univ Calif Berkeley, Dept Chem Engn, Berkeley, CA 94720 USA
[4] Stanford Synchrotron Radiat Lab, Menlo Pk, CA 94025 USA
关键词
D O I
10.1103/PhysRevB.73.115114
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
A temperature-dependent x-ray absorption spectroscopy (XAS) study was performed to investigate the changes in electronic and atomic structure of La-deficient La0.7Sr0.2FeO3-delta (L7S2FO3) and stoichiometric La0.8Sr0.2FeO3-delta (L8S2FO3). La0.8Sr0.2FeO3-delta is a promising cathode material for intermediate operating temperature (700-800 degrees 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 La0.7Sr0.2FeO3-delta (L7S2FO3) and stoichiometric La0.8Sr0.2FeO3-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 Fe3+ and Fe4+ in both L7S2FO3 and L8S2FO3 (mixed valence) as established by comparison with model compounds. Studies from room temperature to 850 degrees C show that Fe3+ dominates over Fe4+ 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 Fe4+ 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.
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页数:9
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