Atomic‐Scale Measurement of Lattice Distortion in Sm‐Doped Bismuth‐Based Oxides

Element doping is an effective strategy to modulate the crystal structure and physical properties of layered oxides. In this work, atomic‐resolution scanning transmission electron microscopy (STEM), combined with high‐angle annular dark‐field (HAADF) imaging and atomic‐resolution energy‐dispersive X‐ray spectroscopy (EDS), was employed to systematically investigate Bi 1.85 Sm 0.15 O 3 (BSO) thin films prepared by spin‐coating. The results show that Sm atoms preferentially occupy the second and fifth atomic layers within each six‐layer unit, forming a long‐range chemically ordered structure and generating a periodic built‐in strain field. The periodic strain further induces local lattice distortion, with the distortion magnitude gradually increasing from approximately 4 pm near the substrate to 22 pm at the film surface. PFM measurements confirm that the films exhibit typical intrinsic ferroelectric characteristics, including butterfly‐shaped amplitude loops, nearly 180° phase switching, and reversible domain switching behavior. This study reveals that doping‐induced local lattice distortion serves as an important pathway for ferroelectric modulation in layered materials, providing atomic‐scale structural insights for optimizing the ferroelectric properties of bismuth‐based oxides.