Oxidation states of Co and Fe in Ba1-xSrxCo 1-yFeyO3-δ (x, y = 0.2-0.8) and oxygen desorption in the temperature range 300-1273 K

Ashley S. Harvey, F. Jochen Litterst, Zhen Yang, Jennifer L.M. Rupp, Anna Infortuna, Ludwig J. Gauckler

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Abstract

Four compositions of Ba1-xSrxCo1-yFe yO3-δ were studied for phase, oxygen uptake-release, and transition metal (TM) oxidation states after solid state processing and with in situ heating from 300 to 1273 K in air. X-Ray diffraction showed that all compositions except one had the cubic perovskite structure at all temperatures; that with x, y = 0.2 was a mixture as prepared, becoming predominantly cubic at high temperature. Thermogravimetry showed a reversible oxygen absorption-desorption of approximately ±1% from 700 to 1273 K. X-Ray absorption and Mössbauer spectroscopy showed a majority TM 3+ valence, with at most 40% TM4+. Up to a temperature of 1073 K, the TM4+ was reduced to TM3+. Further heating of the composition with x, y = 0.2 to 1233 K resulted in the reduction of Co 3+ to Co2+. Results from room temperature measurements confirm the thermally activated carrier hopping mechanism with charge fluctuations, while the high temperature delocalized carrier conductivity occurs with a small amount of TM reduction and without phase change for the initially cubic samples.

Original languageEnglish
Pages (from-to)3090-3098
Number of pages9
JournalPhysical Chemistry Chemical Physics
Volume11
Issue number17
DOIs
StatePublished - 2009
Externally publishedYes

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