Interplay of crystal structure, defect chemistry, and dielectric relaxation in Fe-doped BaTiO3 solid solutions for advanced capacitor applications

Abstract

A series of Fe-doped BaTiO 3 ceramics with varying Fe concentrations (x = 0, 0.5, 1, 2, 4, and 16 %) were successfully synthesized using the sol-gel method, followed by calcination at 1000 °C. X-ray diffraction (XRD) analysis confirmed the formation of a pure perovskite phase for all compositions. Samples with Fe content up to 4 % maintained a tetragonal structure (space group P4mm), whereas the 16 % Fe-doped sample displayed a mixed-phase structure, comprising tetragonal (P4mm) and hexagonal (P6₃/mmc) symmetries, as verified by Rietveld refinement. These structural changes were further supported by Raman spectroscopy, which revealed new vibrational modes indicative of modifications in local symmetry and lattice dynamics. The effect of Fe doping on the dielectric properties was then investigated using complex impedance spectroscopy. The Cole–Cole plots displayed well-defined semicircular arcs; characteristic of Debye-type relaxation dominated by the bulk (grain) response. With increasing Fe concentration, the decreases in arc diameters indicates reduced grain resistance. This trend highlights the influence of Fe substitution on defect chemistry and the enhanced charge carrier mobility within the ceramic matrix. Collectively, these results demonstrate that Fe doping not only modifies the crystal structure and microstructure of BaTiO 3 but also significantly tunes its dielectric response through Debye-type relaxation mechanisms, making these materials promising candidates for multilayer ceramic capacitors (MLCCs). • Successful Synthesis & Phase Formation: Fe-doped BaTiO 3 ceramics with various Fe concentrations were synthesized via the sol–gel method, and XRD confirmed the formation of a pure perovskite phase up to 4 % Fe doping. • Structural Evolution with Doping: Rietveld refinement revealed a tetragonal structure (P4mm) for low Fe content, while 16 % Fe doping induced a mixed tetragonal–hexagonal phase, accompanied by lattice expansion and bonding modifications. • Raman Spectroscopy Insights: The appearance of new vibrational modes in Raman spectra confirmed local symmetry distortions and changes in lattice dynamics induced by Fe incorporation. • Dielectric and Electrical Performance: Impedance spectroscopy showed Debye-type relaxation dominated by bulk response, with reduced grain resistance and enhanced charge carrier mobility at higher Fe levels, making the material promising for capacitors and energy storage.