Lithium-doped nickel ferrite with nominal composition Ni0.5Li0.25Fe2.25O4 was prepared using the sol-gel route. Structural characterization by X-ray diffraction, combined with Rietveld refinement, revealed the formation of a single-phase cubic spinel structure belonging to the \(\:Fd\stackrel{-}{3}m\) space group. The refined lattice constant was found to be 8.347 Å, while the mean crystallite size was estimated to be approximately 54 nm. Li+ ions preferentially occupy octahedral sites, forming an inverse spinel configuration. Scanning electron microscopy revealed homogeneous microstructure with grain size ~ 0.57 μm. UV-Vis-NIR spectroscopy demonstrated a direct optical band gap of 2.33 eV, substantially lower than pristine NiFe2O4, enabling efficient visible-light absorption. X-ray photoelectron spectroscopy verified Ni2+, Fe3+, and Li+ oxidation states. Impedance spectroscopy analysis showed semiconductor behavior with thermally activated conduction exhibiting two activation energies (173 meV below 400 K; 858 meV above 400 K) governed by correlated barrier hopping. Dielectric measurements revealed stable permittivity across wide frequency and temperature ranges with low dielectric losses. Magnetic studies exhibited enhanced saturation magnetization (53.52 emu/g at 300 K) exceeding undoped nickel ferrite, low coercivity (65 Oe) confirming soft magnetic behavior, and microwave operational frequencies in the 10–14 GHz range. These multifunctional properties position Ni0.5Li0.25Fe2.25O4 as a promising candidate for optoelectronic devices, microwave components, and photocatalytic applications.
