Anneal-tuned structural, dielectric and electrical properties of ZnFe₂O₄ nanoparticles synthesized by starch-assisted sol–gel auto-combustion method

Zinc ferrite nanoparticles have been synthesized by sol–gel auto-combustion method using starch as a fuel. The impact of annealing temperature on crystal structure, microstructure and dielectric properties is investigated. The powder X-ray diffraction results demonstrated the formation of well crystalline single cubic phase of zinc ferrite at annealing temperature 400 °C. Increase in crystallinity, crystallite size and lattice parameter were observed with increase of annealing temperature 600 and 800 °C. Field Emission Scanning Electron Microscopy study revealed that the zinc ferrite nanoparticles annealed at 400 °C were spherical with a particle size range 5–30 nm. These particles annealed at 600 °C were also spherical in morphology with a particle size range 10–50 nm. However, zinc ferrite nanoparticles annealed at 800 °C were polyhedron in morphology with particle size range 15–70 nm. The variations of real and imaginary part of dielectric constant, tan δ and AC conductivity are studied at room temperature. The dielectric spectral analysis demonstrated that the dielectric constant is higher at low frequency and decreases with increase in frequency. This dielectric behavior follows the Maxwell–Wagner interfacial polarization. The dielectric constant and dielectric loss tangent of zinc ferrite nanoparticles exhibit dependence on annealing temperature. The impact of annealing temperature is also analyzed through Modulus spectroscopy and Impedance analysis to understand the interaction between grain and grain boundary in zinc ferrite nanoparticles.