Effect of hafnium-incorporation on the microstructure and dielectric properties of cobalt ferrite ceramics

The effect of hafnium (Hf) incorporation on the crystal structure, surface morphology, chemical composition and dielectric properties of cobalt ferrite (CoFe2O4) is reported. Hafnium incorporated Co-ferrite (CoFe2−xHfxO4) ceramics were prepared by varying the Hf concentration in the range of x=0.0–0.2. X-ray diffraction (XRD) studies indicate that the CoFe2−xHfxO4 ceramics crystallize in inverse spinel change to structure similar to that of pure CoFe2O4. Hafnium incorporation induces lattice expansion leading to increased lattice constant from 8.374 Å for pure CoFe2O4 to 8.391 Å for the highest Hf concentration (x=0.2) in CoFe2−xHfxO4. Dielectric constant of CoFe2−xHfxO4 ceramics is also enhanced compared to pure CoFe2O4 due to the lattice distortion upon Hf incorporation. Improved dielectric properties of CoFe2−xHfxO4 ceramics compared to pure CoFe2O4 is attributed to the lattice distortion due to larger Hf-ions substituting for smaller Fe-ions associated structural changes with increased Hf concentration. Frequency variation of the dielectric constant shows the dispersion that can be modeled with a modified Debyeʹs function, which considers the possibility of more than one ion, contributing to the relaxation.