Effect of cation distribution on the structural and dielectric properties of $${\mathrm{N}\mathrm{i}}_{0.5-x}{\mathrm{C}\mathrm{o}}_{x}{\mathrm{Z}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{4}$$ (0.0 ≤ x ≤ 0.5) ferrites

Abstract

Cobalt-substituted nickel–zinc ferrite nanoparticles, i.e., $${\mathrm{N}\mathrm{i}}_{0.5-x}{\mathrm{C}\mathrm{o}}_{\mathrm{x}}{\mathrm{Z}\mathrm{n}}_{0.5}{\mathrm{F}\mathrm{e}}_{2}{\mathrm{O}}_{4}$$ (0.0 ≤ x ≤ 0.5) were prepared by the sol–gel method. X-ray diffraction patterns revealed that the prepared samples crystallized in cubic spinel structure, whereas the scanning electron microscopy study exhibited a change in the morphology of grains due to Co2+ substitution. 57Fe Mossbauer measurements suggested that the presence of iron is only in the Fe3+ oxidation state which is randomly distributed over the tetrahedral and octahedral sites. However, the fraction of Fe3+ ions present at the octahedral site strongly depends on the unusual site preference of substituted Co2+ ions for the tetrahedral site. Thus, the cationic distribution between both the sites altered with increasing Co2+ substitution. Significant enhancement in the resistive properties is found with increasing Co2+ substitution and the obtained values are ~ 104 times higher than that reported for their bulk counterparts. This improvement in the resistive properties is elucidated based on changes in the microstructure and cation redistributions due to Co2+ substitution. Here, we report that the colossal resistivity (3.82 × 1010 Ω cm) and diminished tangent loss (~ 0.01) for the sample with x = 0.2 make this composition interesting for high-frequency applications.