Impact of aluminum substitution on the structural and dielectric properties of Ni–Cu spinel ferrite nanoparticles synthesized via sol–gel route

Aluminum substituted nickel copper Ni 0.5 Cu 0.5 Al x Fe 2 − x O 4 (x = 0.0, 0.2, 0.4 and 0.6) spinel ferrite nanoparticles were prepared via sol–gel auto combustion method. All the samples were annealed at 600 °C for three hours in muffle furnace. The prepared samples were characterized using X-ray diffraction, scanning electron microscopy, Fourier transform infra-red spectroscopy and Impedance Spectroscopy to investigate their structure, morphology and electrical properties. The cubic structure (FCC) with preferred orientation along (311) plane was found with crystallite size of 17–21 nm. Few diffraction peaks corresponding to the secondary phase appear due to insufficient reaction between Al 3+ and Fe 3+ ions. Lattice constant, unit cell volume, dislocation density, stacking fault, lattice strain and micro-strain have been studied as a function of substitution effect. The appropriate substitution is evident from reduction in lattice strain and unit cell volume resulted from significant change in lattice parameters. The real and imaginary parts of dielectric constant, complex modulus, impedance and tangent loss of prepared nanoparticles have been investigated in the frequency range from 100 Hz to 20 MHz. The hopping of charge carriers at higher frequencies would result in improved conduction mechanism for these nanomaterials. Small crystallite size and low dielectric loss of aluminum substituted nickel copper spinel ferrite nanoparticles would make them potential candidate for high storage memory devices, cancer treatment and microwave applications, respectively.