Conductivity and Dielectric Relaxation Properties of Annealed Cr-Substituted Ni-Ferrite Nanoparticles

Nanocrystalline NiCr _x Fe_2?x O₄ spinel samples with x = 0.1 and 0.2 have been synthesized by coprecipitation method and annealed at 620°C and 1175°C for 4 h. Their electrical properties were investigated as functions of frequency in the range of 100 Hz to 100 kHz and temperature in the range of 308 K to 358 K. The dielectric constant (\( \varepsilon^{\prime } \)) and dielectric loss factor (\( {\hbox{tan}}\,\delta \)) appeared to decrease with increasing frequency, while the alternating-current (AC) conductivity (\( \sigma^{\prime } \)) increased. These dielectric parameters increased with increasing temperature. On the other hand, impedance spectroscopy gave Cole–Cole plots with only one semicircular arc for all the samples, indicating that the grain-boundary contribution was dominant in the conduction mechanism.