Impedance Spectroscopic Characterization of Sm and Ho Doped Ni Ferrites

We report on the impedance spectroscopic characterization of Sm and Ho doped Ni ferrite materials, namely and , to demonstrate their improved electrical properties compared to pure NiO. . Sm and Ho doped Ni ferrites crystallize in the cubic inverse spinel phase with a very small amount of and as the additional phase, respectively. Atomic force microscopy measurements indicate that the bulk grains are approximately in size while the grain boundaries are thin compared to bulk grains. Frequency variation of the dielectric constant shows the dispersion that can be modeled with a modified Debye's function, which considers the possibility of more than one ion, contributing to the relaxation. The resistivity values (at ) of , , and compounds are found to be , and , respectively. Impedance spectroscopic analysis indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity , and capacitance of these materials. While the conductivity in pure is predominantly due to intrinsic bulk contribution ( and ), exhibits distinct grain and grain-boundary contributions to the conductivity.