Figure 1

Aberration-corrected HAADF images showing the 90° domain-walls in PbTiO₃ film and electric dipoles formed by the relative displacements of the Ti⁴⁺ and Pb²⁺ cation columns.

(a) HAADF images where the horizontal arrows denote the interface between the PbTiO₃ and SrTiO₃ layers. The blue dotted line traces the ‘head-to-tail’ 90° domain-walls, while the white dotted line denotes the area with ‘head-to-head’ 90° domain-wall (area I). The colored arrows denoted by ‘Ps’ show the directions of the polarization of PbTiO₃ beside the 90° charged-domain-wall. The insets show magnifications of the dipoles formed by the displacements of ions in corresponding domains (yellow: Pb²⁺, red: Ti⁴⁺). Note that, in some PTO units within the area I, no obvious displacement of the Ti⁴⁺ and Pb²⁺ columns are observed, indicating that the polarizations in these unit-cells are restrained. (b) Schematic perspective view of the unit-cell of ferroelectric PbTiO₃. (c) Projection of the unit-cell along the [100] direction showing the δ_Ti. (d) A representative HAADF image of the dipoles in PbTiO₃ crystal. The positions of Pb²⁺ columns are brighter than those of the Ti⁴⁺ columns. δ_Ti is also marked, which is opposite to the spontaneous polarization direction of the PbTiO₃ denoted by the yellow arrow.