Structural, Morphological, Magnetic, and Electrical Properties of ZrFe 2−x Bi x O ₅ Nanoparticles (x = 0, 0.25, 0.50, 0.75 and 1.00) Synthesized via Sol-gel Auto-Combustion

ZrFe 2−x Bi x O 5 (x = 0, 0.25, 0.50, 0.75, 1.00) nanoparticles were synthesized using Sol-gel auto-combustion method and their structural, morphological, magnetic, and frequency-dependent electrical properties were systematically characterized at room temperature. X-ray diffraction analysis confirms single phase monoclinic C2/c formation for every composition, the principal interplanar spacing increases linearly from 2.9503 Å to 3.0034 Å, crystallite size decreases from 32.1 to 16.7 nm, and dislocation density grows nearly four times as x advances to unity. Scanning electron microscopy reveals a progressive transition from large, irregularly agglomerated grains to a finer, more densely packed nanoparticulate microstructure. All M-H loops measured over ±10 kOe identify soft ferromagnetic, multi-domain behavior (S < 0.5 throughout); saturation magnetization plummets from 16.46 to 1.67 emu g −1 while the coercive field rises from 102.24 to 182.22 G. Impedance measurements (100 Hz - 10 MHz) show that bulk resistance increases ten times over the substitution range, Nyquist plots fit to a two element equivalent circuit of two CPE-resistor pairs in series, and the extracted grain and grain-boundary resistances rise monotonically with x, establishing that Bi 3+ incorporation progressively depletes the Fe 3+ /Fe 2+ charge carrier pool. The dielectric constant follows Maxwell-Wagner-Sillars behavior and decreases with both frequency and Bi content, while AC conductivity spectra display a characteristic dual-peak pattern attributed to space-charge polarization at grain boundaries at low frequency and grain-interior Fe hopping at high frequency, both peaks diminishes with increasing Bi content. The correlated structure-property picture presented here establishes the Bi-substituted ZrFe 2 O 5 system as a candidate for compositionally tunable soft-magnetic and dielectric applications.