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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.
- Source :
-
Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2009 May 07; Vol. 11 (17), pp. 3090-8. Date of Electronic Publication: 2009 Feb 11. - Publication Year :
- 2009
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Abstract
- 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.
Details
- Language :
- English
- ISSN :
- 1463-9076
- Volume :
- 11
- Issue :
- 17
- Database :
- MEDLINE
- Journal :
- Physical chemistry chemical physics : PCCP
- Publication Type :
- Academic Journal
- Accession number :
- 19370203
- Full Text :
- https://doi.org/10.1039/b819414a