NANOSIZED FERROELECTRIC CRYSTALS OBTAINED BY A SELF-PATTERNING METHOD

Izabela Szafraniak 1,2Ming-Wen Chu 2,3Marin Alexe 2Dietrich Hesse 2

1. Poznań Technical University, pl. Marii Skłodowskiej-Curie 5, Poznań 60-965, Poland
2. Max Planck Institute of Microstructure Physics (MPI), Weinberg 2, Halle 06120, Germany
3. National Institute of Material Science (NIMS), Tsukuba, Japan

Abstract

The nature of the ferroelectric size effects has been discussed for decades, however, a unified picture is still missing. It seems that interfacial defects play an important role in size effects of ferroelectrics [1]. To investigate this issue we have prepared epitaxial Pb(ZrxTi1-x)O3 nanocrystals with different Zr/Ti ratio (x between 0 and 0.52), in this way providing a lattice mismatch with the SrTiO3 substrate between ~3.4 % and ~0.2%.
Epitaxial PZT nanoislands were prepared by chemical solution deposition onto conductive (001) single-crystal STO:Nb substrates. This method allowed us to prepare uniform and good quality structures and to tune the size of the final structures (i.e. their height can be between 5 and 25 nm). A cross-sectional high-resolution transmission electron microscopy (HRTEM) analysis showed that the PZT nanoislands grown on STO have a truncated-pyramid morphology. The islands are single-crystalline and single-c-domain. Using HRTEM the nature of the misfit dislocations has been analyzed. It turns out that they extend into a PZT region with dimensions as large as ~4 nm in height and ~8 nm in width. Since ferroelectricity is a co-operative phenomenon of a sufficient number of regular noncentrosymmetric unit cells, this significant ratio points to a potential long-range influence on the ferroelectric properties of the PZT nanoislands. Probing the polarization of a large number of bare nanoislands by piezoresponce force microscopy it was found that the PZT (x=0.52) nanoislands with a height of ~9 show an apparent polarization instability. By contrast, the same PZT islands with a height of ~20 nm show well-developed ferroelectricity, as also do tetragonal, epitaxial PbTiO3 nanoislands ~9 nm in height and free from misfit dislocations at the interface.
[1] M.-W. Chu, I. Szafraniak, R. Scholz, C. Harnagea, D. Hesse, M. Alexe, U. Goesele, Nature Materials, 3 (2004) 87.

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Presentation: oral at E-MRS Fall Meeting 2004, Symposium G, by Izabela Szafraniak
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-05-20 14:37
Revised:   2009-06-08 12:55
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