Berlin 2008 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 11: Dielectric and ferroelectric thin films and nanostructures I

DF 11.1: Vortrag

Mittwoch, 27. Februar 2008, 14:00–14:20, EB 107

The impact of strain on the properties of ferroelectric bilayers: A LGD approach — •Ludwig Geske, I.B. Misirlioglu, Ionela Vrejoiu, Marin Alexe, and Dietrich Hesse — Max Planck Institute of Microstructure Physics, Weinberg 2, D-06120

Interfaces and defects may significantly alter the properties of ferroelectric thin films. Epitaxial bilayers consisting of PbZr_0.2Ti_0.8O₃ (PZT20/80) and PbZr_0.4Ti_0.6O₃ (PZT40/60) were grown by pulsed laser deposition with the scope to create defects in a controlled manner in order to investigate their influence. The films were deposited on vicinal SrTiO₃ (001) substrates using a perovskite SrRuO₃ bottom electrode which grows pseudomorphically to the subtrate. A large impact of the layer sequence on the defect generation and the formation of an a/c domain structure can be observed. These structural changes lead to a strong shifting of the remanent polarisation and the dielectric constant. In the attempt to understand this behaviour, the Landau-Ginzburg-Devonshire (LGD) theory is used, which is a versatile tool to describe the behaviour of ferroelectric materials. A short introduction into the LGD theory modified for the treatment of ferroelectric thin films will be given together with the results for single layered PZT20/80 and PZT40/60 films. Subsequently the influence of the electrostatic coupling at the interface between the PZT layers will be demonstrated. Finally the theory will be applied to the specific case of the PZT bilayers on SrTiO₃ to find an explanation for the behaviour of the ferroelectric properties by adapting the possible relaxation states and coupling terms.