Effect of cation distribution on the structural and dielectric properties ofNi0.5-xCoxZn0.5Fe2O4 ferrites

Cobalt-substituted nickel-zinc ferrite nanoparticles, i.e.,Ni0.5-xCoxZn0.5Fe2O4 (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 Co(2+)substitution.Fe-57 Mossbauer measurements suggested that the presence of iron is only in the Fe(3+)oxidation state which is randomly distributed over the tetrahedral and octahedral sites. However, the fraction of Fe(3+)ions present at the octahedral site strongly depends on the unusual site preference of substituted Co(2+)ions for the tetrahedral site. Thus, the cationic distribution between both the sites altered with increasing Co(2+)substitution. Significant enhancement in the resistive properties is found with increasing Co(2+)substitution and the obtained values are similar to 10(4)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 Co(2+)substitution. Here, we report that the colossal resistivity (3.82 x 10(10) omega cm) and diminished tangent loss (similar to 0.01) for the sample withx = 0.2 make this composition interesting for high-frequency applications.