Tunable optical bandgap and dielectric behavior of BaTi1-xFexO3 ceramics: Insights into structural and optical properties

Abstract

• Coexistence of P4mm and P63mmc phases at 16 % Fe doping. • Optical response becomes linear above 4 % Fe substitution. • Bandgap decreases steadily with increasing Fe content. • Higher Fe levels increase Urbach energy and lattice disorder. Polycrystalline (BaTi 1-x Fe x O 3 ) ceramics were successfully synthesized via the sol–gel method using various stoichiometric values of Fe (x = 0, 0.5, 1, 2, 4, and 16 %), followed by calcination at 1000 °C. X-ray diffraction (XRD) analysis revealed that samples primarily crystallize in the tetragonal perovskite phase at low Fe doping levels. However, at a higher Fe concentration ( x = 16 %), a secondary hexagonal phase appears, coexisting with the tetragonal structure. This phase evolution and structural coexistence were further validated through Rietveld refinement, confirming the gradual distortion of the host lattice with increasing Fe incorporation. Scanning electron microscopy (SEM) indicated that the ceramics sintered at elevated temperature exhibit a globular grain morphology, which undergoes noticeable modification at 16 % Fe doping, consistent with the structural phase transition. UV–visible spectroscopy analysis demonstrated a systematic reduction in the optical bandgap energy (Eg), decreasing from 2.63 eV for the undoped sample to 2.35 eV at 16 %. Simultaneously, the Urbach energy (Eu) increased from 1.91 eV to 4.85 eV, reflecting enhanced structural disorder and localized states in the band structure. Furthermore, a transition from nonlinear to linear optical behavior was observed beyond 4 % Fe content, signifying a notable shift in the optical response mechanism. These results underscore the strong potential of Fe-doped BaTiO 3 as a tunable material system for visible-light-driven photocatalytic applications, owing to its adjustable bandgap, enhanced light absorption, and dopant-induced structural flexibility.

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