Article abstract
Nature Materials 6, 64 - 69 (2007)
doi:10.1038/nmat1808
Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films
Chun-Lin Jia1,2, Valanoor Nagarajan3, Jia-Qing He1,2, Lothar Houben1,2, Tong Zhao4, Ramamoorthy Ramesh4, Knut Urban1,2 and Rainer Waser1
Abstract
Typically, polarization and strain in ferroelectric materials are coupled, leading to the generally accepted direct relation between polarization and unit-cell tetragonality. Here, by means of high-resolution transmission electron microscopy we map, on the unit-cell scale, the degree of tetragonality and the displacements of cations away from the centrosymmetry positions in an ultrathin epitaxial PbZr0.2Ti0.8O3 film on a SrRuO3 electrode layer deposited on a SrTiO3 substrate. The lattice is highly tetragonal at the centre of the film, whereas it shows reduced tetragonality close to the interfaces. Most strikingly, we find that the maximum off-centre displacements for the central area of the film do not scale with the tetragonality. This challenges the fundamental belief in a strong polarization–tetragonality coupling in PbTiO3-based ferroelectrics, at such thicknesses. Furthermore, a systematic reduction of the atomic displacements is measured at the interfaces, suggesting that interface-induced suppression of the ferroelectric polarization plays a critical role in the size effect of nanoscale ferroelectrics.
- Institute of Solid State Research, Research Centre Jülich, D-52425 Jülich, Germany
- Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Research Centre Jülich, D-52425 Jülich, Germany
- School of Materials Science and Engineering, University of New South Wales, Sydney NSW, Australia
- Dept of Materials Science and Dept of Physics, University of California, Berkeley, California 94720, USA
Correspondence to: Chun-Lin Jia1,2 e-mail: c.jia@fz-juelich.de
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