Dielectric properties and complex impedance spectroscopy studies of mixed Ni-Co ferrites

Ferrites with general formula Ni(1-x)CoxFe2O4 ( where x = 0.0, 0.2, 0.4, 0.6 and 0.8) were prepared by the conventional double sintering ceramic method. The microstructural features were observed by scanning electron microscopy. An infrared spectroscopy study shows the presence of absorption bands in the higher frequency range around 578 cm(-1) (nu(1)) and in the lower frequency range around 396 cm(-1) (nu(2)); these indicate the presence of tetrahedral and octahedral group complexes, respectively, within the spinel phase. In an effort to understand the conduction mechanism, complex impedance measurements were carried out. The results of complex impedance measurements show that as the cobalt concentration increases, the total impedances (Z' and Z '') decrease. The dielectric permittivity (epsilon') was measured at room temperature (300 K) as a function of frequency from 20 Hz to 1 MHz; it shows the usual dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. Increase of the dielectric permittivity is observed with increase of the cobalt concentration in the nickel ferrite matrix. AC conductivity (sigma(AC)) measurements made in the frequency range 100 Hz-1 MHz suggest that the conduction is due to small polaron hopping.