Direct observation of rotation of polarization at 90-degree domain walls in BaTiO₃

Abstract

The rotation of polarization at 90-degree domain walls in tetragonal BaTiO3 was directly observed by the STEM-CBED method, which combines scanning transmission electron microscopy (STEM) and convergent-beam electron diffraction (CBED). The CBED patterns in the domain wall region exhibit continuous changes in intensity distribution within discs and specific features corresponding to the direction of the rotation of polarization. Simulations were performed using hypothetical superstructures created by continuously connecting Ti displacement with a 90-degree rotation and showed good qualitative agreement with the experimental patterns. The quantitative evaluation of the mirror symmetries existing in the tetragonal structure in bulk form revealed the width of the domain wall is approximately 9 nm. While distorted regions with slightly broken symmetry in CBED disks were found to extend further on both sides of the domain wall region in 6-7 nm. This finding can explain the discrepancy in the domain wall widths reported in previous studies.