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This study introduces a field-based approach to analyze atomically resolved scanning transmission electron microscopy (STEM) images of Sm-doped BiFeO3, employing spatially varying latent Bragg fields to map crystalline order and structural changes. By applying this method across varying Sm concentrations, the researchers reveal a systematic transition from ferroelectric to nonpolar phases, characterized by the emergence of period-doubled order and significant changes in lattice shear and rotation. The findings validate the latent-field reconstruction technique as a powerful tool for understanding phase evolution in ferroelectric materials, offering insights into the interplay between composition and structural properties.
Systematic phase evolution in Sm-doped BiFeO3 reveals a striking transition from extended ferroelectric domains to a connected nonpolar state, driven by composition changes.
Functionalities of ferroelectric materials are governed by the spatial organization and coupling of polarization, strain, lattice rotation, and structural order accessible via atomically resolved scanning transmission electron microscopy (STEM) images. Quantitative interpretation of atomic-resolution STEM data has conventionally relied on locating atomic columns and converting their fitted coordinates into local structural descriptors. Here, we develop a field-based approach in which atomic-resolution images are represented by spatially varying latent Bragg fields, whose amplitudes and phases provide continuous maps of crystalline order, lattice displacement, strain, rotation, and mode-specific residual structure. The observed atomically resolved images are decoded from the latent fields. We apply this framework to image series of Sm-substituted BiFeO3 spanning 0-20% Sm and crossing the composition-driven boundary between the R3c ferroelectric phase and the orthorhombic, nonpolar Pnma phase. Conventional atom-resolved parameterization is used as an independent validation, showing that reconstructed Bragg amplitude tracks local atomic-column intensity and that field-derived shear reproduces unit-cell angular distortions obtained from atom fitting. The combined analysis reveals a systematic evolution from extended ferroelectric domains at low Sm concentration, through the appearance and growth of localized regions with period-doubled Pnma order at intermediate compositions, to a connected Pnma-dominated state at high Sm content. The period-doubled order is accompanied by enhanced shear and lattice rotation and by progressive reorganization of the ferroelectric domain structure. These results establish latent-field reconstruction as a physically interpretable complement to atom finding and provide a unified framework for resolving composition-driven phase evolution in ferroic materials.
