• Meffert, Matthias

Abstract

<jats:title>Abstract</jats:title><jats:p>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-L<jats:sub>3</jats:sub> and Co-L<jats:sub>2</jats:sub> white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L<jats:sub>2,3</jats:sub> 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 Ba<jats:sub>0.5</jats:sub>Sr<jats:sub>0.5</jats:sub>Co<jats:sub>0.8</jats:sub>Fe<jats:sub>0.2</jats:sub>O<jats:sub>3-d</jats:sub> (BSCF), which is hampered by the superposition of the Ba-M<jats:sub>4,5</jats:sub> white-lines on the Co-L<jats:sub>2,3</jats:sub> 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.</jats:p>

Topics

• impedance spectroscopy
• phase
• cobalt
• annealing
• electron energy loss spectroscopy