ISBN 9783843942324

978-3-8439-4232-4, Reihe Werkstoffwissenschaften

Philipp Geiger
Straining Mechanisms in Mixed Ionic/Electronic Conductive Perovskite Ceramics

234 Seiten, Dissertation Universität Erlangen-Nürnberg (2019), Softcover, A5

Zusammenfassung / Abstract

Mixed ionic electronic conductive perovskite ceramics display high oxygen as well as electron conductivity at elevated temperatures. Hence, this material class appears suitable for application as cathodes in solid oxide fuel cells and oxygen separation membranes. The high ionic oxygen conductivity is based on oxygen vacancies. Here, the oxygen vacancy concentration is not a fixed material property but depends on temperature and especially on the oxygen partial pressure and can, therefore, be adjusted. A change of the oxygen stoichiometry is accompanied by a chemical strain, which results in an extraordinarily high effective thermal expansion. As mixed conductive ceramics are often used in sandwich structures, a thermal expansion mismatch between components can result in large mechanical stresses. As such, the goal of this work is to investigate the effect of mechanical stress on the mechanical, structural and functional properties of two different mixed conductive perovskite compounds: LSCF (La0.6Sr0.4)0.95Co0.2Fe0.2O3-d) and BSCF (Ba0.5Sr0.5Co0.8Fe0.2O3-d).

An interesting feature of LSCF is the ferroelastic effect. Ferroelasticity is a non-linear straining mechanism, which is also observed ferroelectric perovskites. The functional properties of ferroelectrics are known to be strongly influenced by oxygen vacancies, although the interaction is not fully understood yet. Since the oxygen non-stoichiometry of LSCF can be manipulated, without changing the overall chemical composition, i.e., by dopants, the characterization of the ferroelastic properties in respect of the oxygen vacancy concentration may allow for new insights on the interaction of oxygen vacancies with ferroelastic/ferroelectric domain walls.