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Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films

Publication Type

Journal Article

Authors

Jia, C.-L., V. Nagarajan, J.-Q. He, L. Houben, T. Zhao, Ramamoorthy Ramesh, K. Urban, R. Waser

DOI

10.1038/nmat1808

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 PbZr"0"."2Ti"0"."8O"3 film on a SrRuO"3 electrode layer deposited on a SrTiO"3 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 PbTiO"3-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. © 2007 Nature Publishing Group.

Journal

Nature Materials

Volume

Year of Publication

2007

ISSN

14761122

Notes

cited By 266

Research Areas

Ramesh Lab