Modulated Double-Switching Characteristics in BiFeO₃ Films via Anion Engineering

Ferroelectric polarization configurations dominate the intrinsic physical properties of ferroelectrics, and underpin advances in strain response, ferroelectric energy storage, and topological electronic devices. Here, low-level sulfur incorporation is proposed as a feasible anion engineering strategy to effectively tune the polarization behavior of BiFeO₃ thin films. At sulfur stoichiometries below 3%, the sulfurized films exhibit distinctive multi-level polarization evolution and unique double-switching characteristics, which are distinct from response of pristine ferroelectric BiFeO₃. Based on synchrotron-based X-ray diffraction, X-ray absorption spectroscopy and Raman spectroscopy, anion-triggered chemical stresses is shown to induce anisotropic lattice distortion and reconstruct the cation-anion coordination environment. Atomic-resolution spherical-aberration-corrected transmission electron microscopy further reveals that sulfurization effectively regulates polarization states and significantly enhances domain heterogeneity, thereby remodeling local polarization configurations. These structural and polarization evolutions collectively create favorable conditions for the emergence of modulated double-switching behavior in sulfurized BiFeO₃ films, highlighting the great potential of anion engineering as an effective yet underexplored strategy to tailor polarization states of ferroelectric materials.