Abnormal Dielectric Behavior in Ti-Ni Spinel Ferrite

The dielectric constant ?' and dielectric loss tangent tan? were investigated as a function of frequency and temperature for the ferrite system TixNi1+xFe2-2xO4 (where 0-x-0.625). It was found that both ?' and tan? decrease with increasing frequency of applied electric field. The behavior of the dielectric constant with frequency was explained on basis of hopping mechanism and Koops theory. It is noticed that dielectric constant decreases with increasing temperature up to certain temperature TMS after that increase. Then the metal/semiconductor transition temperature, TMS, was determined from ?'(F, T) plots. The loss tangent tan? showed an abnormal behavior (loss peaks) with temperature and frequency for the pure and low substitution for the studied system. The loss peaks shifts to higher values of frequencies as temperature increases. The activation energy for dielectric relaxatio showed an increase with increasing Ti and Ni contents. An attempt is made to explain the metallic like behavior and abnormal relaxation loss for the samples.