Synthesis and characterization of Cr doped CoFe₂O₄

Polycrystalline samples of pure and Cr-doped cobalt ferrite (CoFe₂O₄ and CoCrFeO₄) were prepared by solid state reaction route method. X-ray diffraction pattern infers that both the samples are in single phase with Fd3m space group. Slight reduction in the lattice parameter of CoCrFeO₄ has been observed as compared to CoFe₂O₄. The dielectric dispersion has been explained on the basis of Fe²⁺ ↔ Fe³⁺ hopping mechanism. The polarizations at lower frequencies are mainly attributed to electronic exchange between Fe²⁺ ↔ Fe³⁺ ions on the octahedral site in the ferrite lattice. In the present system a part from n-type charge carrier (Fe³⁺/Fe²⁺), the presence of (Co³⁺/Co²⁺) ions give rise to p-type charge carrier. Therefore in addition to n-type charge carrier, the local displacement of p-type charge carrier in direction of external electric field also contributes to net polarization. However, the dielectric constant and loss tangent of CoCrFeO₄ are found to be lower than CoFe₂O₄ and is attributed to the availability of ferrous ion. CoCrFeO₄ have less amount of ferrous ion available for polarization as compared to that of CoFe₂O₄. The impedance spectra reveal a grain interior contribution to the conduction process.