Microstructure, optical and dielectric properties of cobalt-doped zinc ferrite nanostructures

In the present work, we have explored the physical properties of ZnFe2-xCoxO4 (0 <= x <= 0.06) nanoferrites synthesized via a simple sol-gel auto combustion process. The microstructure, optical, dielectric and thermal properties were studied through various analytical techniques. The X-ray diffraction (XRD) data were analyzed through the Rietveld refinement program, confirming the cubic spinel structure with Fd-3m space group and no extra impurities or other secondary phases are present in the samples. The surface morphology was studied through scanning electron microscopy (SEM) that shows a uniform surface along with agglomeration of the particles and the energy dispersive X-ray (EDX) analysis manifests the chemical composition in the samples. The average crystallite size is calculated with the help of Scherrer equation and is found to lie in the nanoscale range. Fourier transform infrared (FTIR) spectroscopy confirms the bending/stretching modes related to the functional groups at different wavenumbers. The optical properties have been studied with the help of UV-visible absorption spectra that show a redshift in the Co-doped ZnFe2O4 samples. This shift may be due to the generation of extra energy states within the bandgap. A slight variation (2.23 eV to 2.18 eV) in the optical bandgap is observed with the increase in Co doping. The dielectric constant is found to vary with the increase in frequency at room temperature. The higher values of the dielectric constant at lower frequencies can be understood on the basis of Maxwell-Wagner model. Our results conclude that the creation of oxygen vacancies plays a significant role and doping of Co ions affects the various physical properties of ZnFe2O4 nanostructures.