Properties of Al3+ substituted nickel ferrite (NiAlxFe2-xO4) nanoparticles synthesised using wet sol-gel auto-combustion

Currently, spinel ferrites are of great interest due to their large range of practical high frequency applications. Nickel spinel ferrites with formula NiAlxFe2-xO4 (where x = 0.0, 0.05, 0.10, 0.15, 0.20, 0.25) were prepared by a wet chemical sol-gel auto-combustion method. All the samples were annealed at 600 °C for 3 h and pellets were made to investigate the dielectric properties. The spinel structure of the nickel-based ferrites was confirmed by using X-rays diffraction analysis. The crystallite size was estimated using Scherrer’s formula and observed to be in the range from 11 to 17 nm. The addition of Al3+ varies the lattice constant from 8.26 to 8.35 A. The study of dielectric properties of interest (complex dielectric constant, dielectric tangent loss, impedance, A.C. conductivity, and electric modulus) as a function of the Al doping concentration was carried out in the frequency range from 1 MHz to 3 GHz using an impedance analyser. On the basis of these investigations, it was found that both the real and imaginary parts of the dielectric constant decreased with increasing applied frequency. Cole–Cole plots of electric modulus revealed evidence of contribution from grains and grain boundaries in the conduction mechanism. The observations revealed that with increasing aluminium doping, the dielectric properties of these ferrite materials are 6.