Cobalt-substitution effects on dielectric properties of CuZn ferrites

The effects of cobalt oxide addition on the microstructure and electrical properties of CuZn ferrites were investigated. CuZn ferrites with compositions of (CuO)_0.2(ZnO)_0.8-x(Co₂O₃)_x/2 (Fe₂O₃)_0.986; x=0, 0.02, 0.04, 0.08, 0.1 were synthesized using a solid state reaction. It was observed that the addition of cobalt will change the amounts and distribution of Cu²⁺, Cu⁺, Fe²⁺, and Fe³⁺ in the grain and grain boundary. The different amounts and distribution of Cu²⁺, Cu⁺, Fe²⁺, and Fe³⁺ in the bulk and grain boundary for samples added with different amounts of cobalt oxide affected the space polarization and dielectric properties. The dielectric constant increased and reached the maximum as the x value was increased from 0 to 0.04 and then declined with further increasing the x value to 0.1. For the samples with the x value of 0.02, the substitution of Co³⁺ may act as a donor and simultaneously produce electrons. Fe³⁺ ions in the octahedral sites catch the electrons and then become Fe²⁺ ions, which led to the larger dielectric constant at low frequency resulting from the space charge polarization. However, as the x value increased to 0.1, the concentration of Fe²⁺ ions decreased, which resulted in a decrease in the amount of space charge in the grains, leading to a decrease in the dielectric constant at low frequency.