Extended Data Fig. 6: Distortion of oxygen octahedron in BFO during domain-wall migration.
From: In-plane charged domain walls with memristive behaviour in a ferroelectric film
a, The integrated differential phase contrast (iDPC) STEM image of the uniformly polarized state. Inset presents unit cell schemes with Bi, Fe, O, Sr, and Ru atoms (red, green, blue, yellow, and dark blue, respectively). Polarization vectors are presented by blue and red arrows at left. b, The iDPC-STEM image of “tail-to-tail” polarized state with schemes of atoms and polarization vectors. Scale bars (a,b), 1 nm. c, The distances of top and bottom oxygen atoms for each BFO layer in “tail-to-tail” state from experimental and calculation results. The error bars are the standard error of mean in each layer. d, The comparison of experiment and DFT calculation off-centre displacement of oxygen octahedra and Fe atoms for each BFO layer in “tail-to-tail” state. Off-center displacement is defined as a distance from the centre of oxygen octahedra (or Fe atoms) to the center of the Bi lattices. Along with the accumulation of oxygen vacancies, the distortion of oxygen octahedra in BFO is also observed. The positions of oxygen atoms are precisely determined using iDPC-STEM imaging technique. Using a 4-quadrant detector, the iDPC-STEM imaging technique can observe both light and heavy elements with clear contrast. The light elements have a higher signal to dose ratio in iDPC imaging, which makes oxygen visible43. In the tail-to-tail state, the distances between the top and bottom oxygen atoms are decreased at the domain wall, showing a clear compression of oxygen octahedra. Accompanied by the compression at the domain wall, oxygen octahedra at the BFO/SRO interfaces are stretched, leading to larger off-centre displacements. The lattice deformation across the domain wall is further confirmed by our DFT calculations (Fig. S7c,d), which demonstrate the quantitative agreement with experimental data. Previous works also indicated that missing oxygen atoms in perovskite unit cells lead to oxygen octahedra to be compressed44,45. The observed lattice distortion and the accumulation of oxygen vacancies around the tail-to-tail domain wall are the structural and electrical factors for the creation and manipulation of charged domain wall, respectively.
