Structure, electrical, and optical properties of Co0.7-xZnxNi0.3Fe2O4 (0.3 ≥ x ≥ 0.7) nano-ferrite by sol–gel auto-combustion technique

Abstract Zn 2+ doped Ni 0.3 Zn x Co 0.7-x Fe 2 O 4 (0.3 ≥ x ≥ 0.7) spinel nanoparticles were synthesized via Sol–gel-auto combustion methods using EDTA and citric acid as fuel. XRD, Raman spectroscopy, FE-SEM, and EDX demonstrated that samples possessed a well-crystalline cubic spinel structure. Both crystallite size and the lattice parameter values increased due to the smaller ionic radius of Co 2+ -ions compared to the Zn 2+ ionic radius. The crystallite size average values ranged from 24–50 nm while lattice parameters were between 8.3877 Å and 8.4268 Å. The surface morphological variation and the elements supplied were analyzed using FE-SEM and EDX, displaying spherical-shaped nanoparticles and all constituent elements. Based on the results of the optical properties, raising Zn 2+ caused the refractive index and the reflectance to rise. The dielectric constant and dielectric loss of Ni 0.3 Zn x Co 0.7-x Fe 2 O 4 reduced substantially with increasing frequency. Moreover, the increase in Zn 2+ concentration causes the decrease in dielectric constant due to Fe 3+ -ion migration from the hopping procedure, which decreases the hopping process (Fe 2+ and Fe 3+ -ions) according to Koop's theory (Maxwell–Wagner polarization). The maximum dielectric constant, reported at x = 0.7 (no Co 2+ -ions), may be related to the generation of Fe 2+ -ions occupying octahedral sites. This leads to an increase in Fe 2+ and Fe 3+ electron exchange, polarization, and conductivity enhancement. These results revealed that Ni 0.3 Zn 0.7x Fe 2 O 4 has a high capacitance and loss, making it promising option for electronic equipment such as computer memory cards, microwave absorbers and capacitors.