Cr-site engineering of BaFeO3 perovskites: correlating structural defects, electronic structure, optical response and charge transport

Abstract

Ba_1−xCr_xFeO₃ (x = 0.1–0.4) perovskite ceramics were synthesized by the solid-state reaction method to investigate the role of Cr-site substitution in modulating their structural, optical, dielectric, and vibrational properties. X-ray diffraction confirmed the retention of the BaFeO₃-type perovskite framework, while Williamson–Hall, Halder–Wagner, modified Scherrer, and size–strain plot analyses revealed pronounced method-dependent crystallite-size estimates and composition-dependent lattice distortion. The SSP, stacking fault, lattice strain, and dislocation density analyses further indicated that BCF3 possesses comparatively lower structural disorder, whereas BCF4 exhibits the highest lattice distortion and defect density. The optical bandgap showed a non-monotonic composition dependence, decreasing to a minimum of 2.948 eV for Ba_0.8Cr_0.2FeO₃ before increasing with further Cr incorporation, demonstrating composition-sensitive modification of the electronic structure and enhanced visible-light response at x = 0.2. The dielectric response exhibited pronounced frequency dispersion, particularly at low frequencies, consistent with interfacial polarization and defect-assisted charge transport. FTIR analysis confirmed Fe–O/Cr–O vibrations and progressive modification of the local FeO₆/CrO₆ octahedral environment with increasing Cr content. Overall, the results demonstrate that Cr-site engineering provides a controllable means of coupling lattice distortion with optical and dielectric responses while preserving the BaFeO₃ perovskite framework. This composition-dependent tunability highlights Cr substitution as an effective strategy for tailoring the functional properties of BaFeO₃-based ceramics.