@article{33623,
  keywords = {Transmission electron microscopy, Electrodes, Polarization, Ferroelectricity, Interfaces (materials), Ultrathin films, Nanoscale ferroelectrics, Off-centre displacements},
  author = {C.-L Jia and V Nagarajan and J.-Q He and L Houben and T Zhao and Ramamoorthy Ramesh and K Urban and R Waser},
  title = {Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films},
  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.},
  year = {2007},
  journal = {Nature Materials},
  volume = {6},
  number = {1},
  pages = {64-69},
  publisher = {Nature Publishing Group},
  issn = {14761122},
  doi = {10.1038/nmat1808},
  note = {cited By 266},
  language = {eng},
}