Electrical and dielectric properties of Ni0.5Co0.5GaxFe1.8–xO4 (x ≤ 1.0) spinel ferrite microspheres

Abstract

Microspheres of Ni0.5Co0.5GaxFe2−xO4(x≤1.0) microsphere spinel ferrites (NiCoGaFe-MSFs) and carbon spheres were prepared via a hydrothermal technique. The microstructure of microspheres was investigated through scanning and transmission electron microscopy (SEM and TEM), respectively, and X-ray diffraction (XRD). The electrical and dielectric properties of NiCoGaFe-MSF at temperatures ranging from 20 to 120 °C (between 293.1 × 103 and 393.1 × 103) for f ≤ 3.0 MHz were systematically studied as a result of 3D graphical drawing of the data obtained from an impedance analyzer. Relevant parameters such as ac/dc conductivity, dielectric loss, dielectric constant, activation energy, dissipation factor and Cole–Cole impedance spectra were extensively evaluated for various Ga ion mole ratios in the substitution where x≤1.0. We notice that the ac conductivity mostly obeys exponential power law rules, which vary significantly with the substitution ratios of Ga ions. Impedance analyses confirm that differences in conduction mechanisms in NiCoGaFe-MSFs are mainly due to grain-to-grain boundaries related to Ga ion substitution ratios. The change in dielectric constant of NiCoGaFe-MSFs is strongly dependent on the substitution rates and results in a normal dielectric distribution with frequency. The tangential loss for all microspheres is observed to vary with measured temperatures and their frequency dependencies can be attributed to the conduction mechanism similar to Koop's phenomenological model. It is clearly seen that the formation of semicircles is dominated by all the NiCoGaFe-MSFs and the diameter of the semicircles mostly decreases with increasing temperature, as evidence of a temperature-dependent relaxation mechanism.