Impact of Al³⁺ substitution on structural, Raman, transport electromagnetic properties of LiFe₂O₄ nanoparticles

Nanocrystalline Li_0.5Al_xFe_2.5-xO₄(x = 0.0 to 0.8 in steps, x = 0.2) compounds were prepared using the sol-gel auto-combustion technique. X-ray diffraction (XRD) analysis confirmed the single-phase cubic spinel structure, which showed that the lattice constant changed significantly, especially in the x = 0.6 sample, where it decreased clearly. The crystallite size decreased with increasing Aluminium content, reaching a small value of about 5 nm for the composition x = 0.8 sample. Raman peaks of pure LiFe₂O₄ were determined in both phases (alpha and beta), while smaller peaks at 198 and 236 cm⁻¹ that related to the alpha phase were distinguished. All peaks diminished in intensity after Al³⁺ ions were doped to LiFe₂O₄ except for the peak at 700, where it became predominantly. The bandgap of the samples was deduced and analyzed from Tauc's plot according to UV–Vis spectra. The change in the electronic structure of the Li-Al ferrites, at which the size of the ferrite becomes close to the de Broglie wavelength, results in a band gap for the Al replaced by LiFe₂O₄ with different electronic configurations. The variation of the fundamental part of the dielectric constant (ε′), loss tangent (tan δ), and AC conductivity with frequency has been discussed with composition. The increase in Al³⁺ ion content affected the coercive force, as it decreased, while the saturation magnetism increased when adding Aluminium (x = 0.2) and then began to decline gradually.