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MM: Fachverband Metall- und Materialphysik

MM 21: Topical Session: TEM-Symposium - HR Imaging & Analytic II

MM 21.2: Vortrag

Dienstag, 12. März 2013, 12:00–12:15, H4

Electron microscopy study of Y-doped BSCF — •Matthias Meffert¹, Philipp Müller^1,3, Heike Störmer¹, Christian Niedrig², Stefan F. Wagner², Ellen Ivers-Tiffée^2,3, and Dagmar Gerthsen^1,3 — ¹Laboratorium für Elektronenmikroskopie, KIT, Karlsruhe, Germany — ²Institut für Werkstoffe der Elektrotechnik, KIT, Karlsruhe, Germany — ³DFG Center for Functional Nanostructures, KIT, Karlsruhe, Germany

Mixed ionic-electronic conducting ceramic membranes are well suited for oxygen separation. The cubic phase of perovskite Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) has received particular attention due to its high oxygen permeability. However long-term phase stability at application relevant temperatures (700 - 800 ^∘C) is still an issue to be solved. Oxidation of the B-site cation cobalt and a concurrent decrease of ion radius cause a slow decomposition of the cubic BSCF phase. Beside the hexagonal phase precipitates with plate-like morphology are formed which consist of a mixture of different phases.
To improve the stability of the cubic BSCF phase doping with yttrium was investigated using analytical transmission electron microscopy and scanning electron microscopy. Y-doping suppresses the formation of cobalt oxide precipitates which serve as nucleation centers for plate-like precipitates and the hexagonal phase in undoped BSCF. Hence, the hexagonal phase is only formed at grain boundary triple points (800 ^∘C) and decorates most grain boundaries at 700 ^∘C. Samples annealed at elevated temperatures (≥900 ^∘C) are free of secondary phases in contrast to undoped material.