Role of Al^3 + ion substitution in modulating conductivity and interfacial polarization in CoNiCuZn spinel ferrite: Cation distribution study

The current study examines the effect of Al³⁺ ion substitution (x = 0.00 – 0.10) on the electrical and dielectric properties of host Co_0.25Ni_0.25Zn_0.25Cu_0.25Fe₂O₄ spinel ferrite nanoparticles (Al → CoNiZnCu SFNPs) which have been synthesized via sol-gel auto combustion method . XRD (X-ray powder Diffraction) analysis confirmed the cubic spinel structure of all products. The crystallite size (D_XRD) varies between 35 and 36 nm. AC conductivity increased with frequency (f) and temperature (T), confirming polaron hopping mechanisms. Al³ ⁺ ion substitution altered charge transport by disrupting Fe²⁺–Fe³ ⁺ hopping, increasing resistivity up to x = 0.06 and slightly recovering at higher x due to microstructural effects. Activation energies (Ea), derived from Arrhenius plots, peaked at x = 0.06 and decreased at both extremes, reflecting variable charge mobility. The dielectric constant (ε′) showed strong frequency (f) dispersion and Temperature (T) dependence, decreasing with Al³ ⁺ ion content but rising again at x = 0.08. Dielectric loss (tan δ) revealed relaxation peaks and high loss values at x = 0.06 and 0.10, indicating interfacial polarization and grain boundary conduction. Cole–Cole impedance plots confirmed non-Debye relaxation with dual grain and grain boundary contributions, shifting with Al³ ⁺ ion content and T . These findings confirmed that Al³ ⁺ ion substitution can effectively tune the electrical & dielectric behavior of host Co _0.25 Ni _0.25 Zn _0.25 Cu _0.25 Fe ₂ O ₄ SFNPs for functional device applications.