Regensburg 2004 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 6: Nanostrukturen, Schichten und Keramiken
DF 6.4: Vortrag
Donnerstag, 11. März 2004, 11:10–11:30, H11
The contribution of misfit dislocations to polarization instabi-lities of epitaxial ferroelectric Pb(Zr0.52Ti0.48)O3 nanoislands — •D. Hesse, M.-W. Chu, I. Szafraniak, R. Scholz, C. Harnagea, and M. Alexe — Max-Planck-Institut für Mikrostrukturphysik Halle
(001)-oriented Pb(Zr0.52Ti0.48)O3 (PZT) epitaxial nanoislands of d≈9 nm average height were grown on niobium-doped SrTiO3 (001) substrates (STO:Nb) by chemical solution deposition (CSD) at 800∘C. Due to the lattice mismatch, edge-type misfit dislocations are formed at the PZT/STO:Nb interface. Using high-resolution electron microscopy (HREM), the nature of these misfit dislocations has been analyzed, resulting in a Burgers vector b a⟨100⟩. Applying the geometric phase imaging method of quantitative HREM, the asymmetric strain fields of the misfit dislocations have been visualized. It turns out that they extend into a PZT region with dimensions as large as ∼ 4 nm in height and ∼ 8 nm in width. Within this region the lattice deviates from the regular PZT crystal structure, implying a reduced or even vanishing spontaneous polarization. Piezoresponse force microscopy indicates that PZT nanoislands of d≈9 nm indeed do not show ferroelectricity, whereas PZT islands of d≈20 nm and also misfit dislocation-free PbTiO3 islands of d≈9 nm are ferroelectric. It is concluded that a stable polarization in nanostructured ferroelectrics requires misfit engineering.