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 Ni O . Fe 1.925 Sm 0.075 O 3 and Ni O . Fe 1.925 Ho 0.075 O 3 , to demonstrate their improved electrical properties compared to pure NiO. Fe 2 O 3 . Sm and Ho doped Ni ferrites crystallize in the cubic inverse spinel phase with a very small amount of Sm Fe O 3 and Ho Fe O 3 as the additional phase, respectively. Atomic force microscopy measurements indicate that the bulk grains are approximately 2 – 5 μ m 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 3.5 KHz ) of Ni O . Fe 2 O 3 , Ni O . Fe 1.925 Sm 0.075 O 3 , and Ni O . Fe 1.925 Ho 0.075 O 3 compounds are found to be 0.1 × 10 4 Ω m , 0.5 × 10 4 , Ω m and 0.8 × 10 4 Ω m , respectively. Impedance spectroscopic analysis indicates the different relaxation mechanisms and their variation with temperature, bulk grain and grain-boundary contributions to the electrical conductivity ( R g ) , and capacitance ( C g ) of these materials. While the conductivity in pure Ni Fe O 4 is predominantly due to intrinsic bulk contribution ( R g = 213 k Ω and C g = 4.5 × 10 − 8 F ), Ni O . Fe 1.925 R 0.075 O 3 ( R = Sm , Ho ) exhibits distinct grain and grain-boundary contributions to the conductivity.