Three-Dimensional Pseudo-Ferroelectric Domain Walls in BiFeO₃: Atomic-Scale Oxygen Octahedral Rotation and Polar...

The emergence of multiferroic order in perovskite thin films is governed by symmetry-broken coupling between polar domains and magnetic order parameters; however, currently prevailing theoretical frameworks, due to a constraint of reduced-dimensional approximations, fail to capture the inherent three-dimensional (3D) complexity of domain-mediated cross-correlations. Here, performing atomic-resolution HAADF/iDPC-STEM on BiFeO₃ (BFO), we discover a "pseudo-ferroelectric domain wall" bridging (1$\overline{1}\overline{4}$)_h/($\overline{1}\overline{1}$0)_h planes of BFO, in which two-dimensional (2D) projection indicates a domain-wall angle of 54.37°, but the actual 3D orientation remains 70.17°. When the (1$\overline{1}\overline{4}$)_h plane is rotated 90° about the [2$\overline{2}1$]_h axis, it reveals the atomic arrangement of the ($\overline{1}\overline{1}$0)_h plane, with polarization along [00$\overline{1}$]. These noncanonical 3D walls arise from oxygen-rearrangement-induced structural deviations and asymmetric Fe-O lattice coupling, which generate chiral polarization stabilized by a potent tripartite interaction between ferroelectric, shear, and spin degrees of freedom. This work provides a design principle for reconfigurable domain wall nanoelectronics.