Engineering Pseudo‐c/a Twin Boundaries in Super‐Tetragonal BiFeO ₃ for Domain‐Wall Nanoelectronics

ABSTRACT Ferroelectric domain walls have emerged as promising building blocks for next‐generation nanoelectronics. Recent studies have revealed that large‐angle c/a twin boundaries in lead‐based ferroelectric thin films exhibit superior physical properties, including enhanced piezoelectric responses, flexoelectric effects, and multi‐caloric behaviors. However, the realization of analogous c/a ferroelastic structures in lead‐free BiFeO ₃ (BFO) thin films remains challenging. Here, we report the successful construction of coherent pseudo‐c/a twin domain walls in highly tetragonal Ga‐doped BFO thin films. These domain boundaries are found to accommodate cross‐hatched polarization arrays that effectively compensate domain wall electrostatics, along with a markedly enhanced flexoelectric effect. Moreover, these twin boundaries exhibit polarization‐gated switchable conductivity, highlighting their potential for use in memory devices. Our work offers new insights into the design of large‐angle ferroelectric domain walls and lays a foundation for future domain‐wall‐based electronic applications.