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Title: 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

Abstract

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 frommore » 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.« less

Authors:
; ; ;  [1];  [2];  [3];  [2]
  1. Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 (United States)
  2. (United States)
  3. (United States) and Department of Chemical Engineering, University of California, Berkeley, California 94720 (United States)
Publication Date:
OSTI Identifier:
20788001
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 73; Journal Issue: 11; Other Information: DOI: 10.1103/PhysRevB.73.115114; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, 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

Citation Formats

Deb, Aniruddha, Ralph, James M., Cairns, Elton J., Bergmann, Uwe, Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, and Stanford Synchrotron Radiation Laboratory, Sand Hill Road, Menlo Park, California 94025. 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. United States: N. p., 2006. Web. doi:10.1103/PHYSREVB.73.1.
Deb, Aniruddha, Ralph, James M., Cairns, Elton J., Bergmann, Uwe, Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, & Stanford Synchrotron Radiation Laboratory, Sand Hill Road, Menlo Park, California 94025. 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. United States. doi:10.1103/PHYSREVB.73.1.
Deb, Aniruddha, Ralph, James M., Cairns, Elton J., Bergmann, Uwe, Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, and Stanford Synchrotron Radiation Laboratory, Sand Hill Road, Menlo Park, California 94025. Wed . "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". United States. doi:10.1103/PHYSREVB.73.1.
@article{osti_20788001,
title = {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},
author = {Deb, Aniruddha and Ralph, James M. and Cairns, Elton J. and Bergmann, Uwe and Chemical Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 and Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720 and Stanford Synchrotron Radiation Laboratory, Sand Hill Road, Menlo Park, California 94025},
abstractNote = {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.},
doi = {10.1103/PHYSREVB.73.1},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 11,
volume = 73,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}