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DF: Dielektrische Festkörper

DF 3: Poster Session

DF 3.1: Poster

Monday, March 27, 2006, 09:30–17:00, P1

Domain structures, grain boundaries and PTCR effect of ferroelectric barium titanate ceramics — •Michael Roessel, Mihail Dan Croitoru, David Moser, and Oliver Eibl — Institut fuer Angewandte Physik, Eberhard Karls Universitaet Tuebingen, Auf der Morgenstelle 10, D-72076 Tuebingen, Germany

Perovskite materials such as barium titanate have many applications as electronic devices. During the cubic to tetragonal phase transition at Tc (393K) BaTiO3 exhibits a strong non-linear change of the electrical resistivity (PTCR effect) caused by grain boundaries. The PTCR effect appears in semiconducting barium titanate and is determined by the microstructure of the material. The Heywang model explains the PTCR jump by the existence of a Schottky barrier at the grain boundaries. This model assumes 180^∘ domains, compensating space charges at the grain boundaries. Our TEM studies by diffraction contrast under two-beam and many beam diffraction conditions show irregularly arranged 90^∘ domains. For the analysis of the grain boundaries we concentrate on grains that are close to a pseudocubic [100] orientation. So far 180^∘ domains were not observed experimentally. Compressive stresses in curved sections of the grain boundaries yield a sub-µm domain structure. The appearance of such domain structures might be explained by compensating mechanical stresses during the cubic to tetragonal phase transition. Therefore, Heywangs model is an oversimplification and does not contain a realistic structural model for explaining the electrical resistivity of barium titanate. The goal of our work is a better understanding of the PTCR effect based on an improved grain boundary structure model.