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Microsc Microanal. 2013 Dec;19(6):1595-605. doi: 10.1017/S1431927613013536. Epub 2013 Oct 16.

Fast mapping of the cobalt-valence state in Ba0.5Sr0.5Co0.8Fe0.2O3-d by electron energy loss spectroscopy.

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  • 1Laboratorium für Elektronenmikroskopie, Karlsruher Institut für Technologie (KIT), Engesserstraße 7, 76131 Karlsruhe, Germany.

Abstract

A fast method for determination of the Co-valence state by electron energy loss spectroscopy in a transmission electron microscope is presented. We suggest the distance between the Co-L3 and Co-L2 white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L2,3 white-line distance can be automated and is therefore well suited for the evaluation of large data sets that are collected for line scans and mappings. Data with a low signal-to-noise due to short acquisition times can be processed by applying principal component analysis. The new technique was applied to study the Co-valence state of Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), which is hampered by the superposition of the Ba-M4,5 white-lines on the Co-L2,3 white-lines. The Co-valence state of the cubic BSCF phase was determined to be 2.2+ (±0.2) after annealing for 100 h at 650°C, compared to an increased valence state of 2.8+ (±0.2) for the hexagonal phase. These results support models that correlate the instability of the cubic BSCF phase with an increased Co-valence state at temperatures below 840°C.

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