TY - JOUR
KW - Transmission electron microscopy
KW - Electrodes
KW - Polarization
KW - Ferroelectricity
KW - Interfaces (materials)
KW - Ultrathin films
KW - Nanoscale ferroelectrics
KW - Off-centre displacements
AU - C.-L Jia
AU - V Nagarajan
AU - J.-Q He
AU - L Houben
AU - T Zhao
AU - Ramamoorthy Ramesh
AU - K Urban
AU - R Waser
AB - 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.
BT - Nature Materials
DO - 10.1038/nmat1808
LA - eng
M1 - 1
N1 - cited By 266
N2 - 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.
PB - Nature Publishing Group
PY - 2007
SP - 64
EP - 69
T2 - Nature Materials
TI - Unit-cell scale mapping of ferroelectricity and tetragonality in epitaxial ultrathin ferroelectric films
VL - 6
SN - 14761122
ER -