  Chromium substituted cobalt ferrite with grain size less than the single
domain (approx. 70 nm) has been prepared by the sol-gel method. XRD analysis
reveals that the samples crystallize to cubic symmetry with spacegroup number
227. Two transition temperatures (TD (approx. 450 K) and TM (approx. 600 K)
have been observed from the impedance verses temperature measurement. TD
increases with the increase in frequency due to dipole response to the
frequency. TM is comparable with the para-ferrimagnetic transition temperature
of cobalt ferrite, which is independent of frequency. This result is well
supported by the temperature dependent DC conductivity measurement. The
modified Debye relaxation could be explained the impedance spectra of
CoFe2-xCrxO4. The grain and grain boundary effect on impedance spectroscopy has
been observed from Cole-Cole analysis. The ac conductivity follows Arrhenius
behavior at different frequencies. All the samples exhibit the negative
temperature coefficient of resistance behavior which reveals the semiconducting
behavior of the material. The Mott VRH model could explain the DC electrical
conductivity. Both ac impedance and DC resistivity are well co-related each
other to explain the electron transport properties in Cr substituted cobalt
ferrite. The electrical transport properties could be explained by the electron
hopping between different metal ions via oxygen in the material.
