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Oxidation states of Co and Fe in Ba(1-x)Sr(x)Co(1-y)Fe(y)O(3-delta) (x, y = 0.2-0.8) and oxygen desorption in the temperature range 300-1273 K

, : Oxidation states of Co and Fe in Ba(1-x)Sr(x)Co(1-y)Fe(y)O(3-delta) (x, y = 0.2-0.8) and oxygen desorption in the temperature range 300-1273 K. Physical Chemistry Chemical Physics 11(17): 3090-3098

Four compositions of Ba(1-x)Sr(x)Co(1-y)Fe(y)O(3-delta) 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% TM(4+). Up to a temperature of 1073 K, the TM(4+) was reduced to TM(3+). Further heating of the composition with x, y = 0.2 to 1233 K resulted in the reduction of Co(3+) to Co(2+). 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.


PMID: 19370203

DOI: 10.1039/b819414a

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