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Lead-free ferroelectric materials with a tetragonal tungsten bronze (TTB) structure have attracted increasing attention due to their multifunctional potential in microelectronics and energy applications. In this study, Ba(2–x)Sr(x)GdFeNb₄O₁₅ (x = 0, 1, 2) ceramics were synthesized via the solid-state reaction route to investigate the influence of Sr substitution on structural and dielectric behaviors. X-ray diffraction combined with Rietveld refinement confirmed the formation of a single TTB phase with space group P4/mbm, showing a systematic decrease in lattice parameters with increasing Sr content, attributed to the smaller ionic radius of Sr²⁺ compared to Ba²⁺. Raman and FTIR spectroscopies evidenced characteristic vibrational modes of the MO₆ octahedra, reflecting subtle structural distortions upon substitution. SEM analysis revealed dense microstructures with grain sizes varying from 2 to 14 μm, depending on the Sr concentration. Dielectric measurements demonstrated a high dielectric constant, low losses, and a sharp permittivity peak near the Curie temperature (≈310–330 °C), typical of classical ferroelectric behavior. The Curie–Weiss analysis indicated a second-order phase transition with large Curie constants (C > 10⁴), confirming the displacive nature of the transition. These findings highlight the significant tunability of TTB-type Ba–Sr–Gd–Fe–Nb oxides for potential applications in capacitors, sensors, and multifunctional electronic devices.
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