Electrical Properties of High-Density Iron-Deficient Nickel-Zinc Ferrites

The dc resistivity of nickel-zinc ferrite was studied as a function of nickel/zinc ratio, apparent density, temperature, and grain size. Resistivities of Ni_0.40Zn_0.51Fe_1.90O₄– and Ni_0.35Zn_0.65-Fe_1.90O₄– are similar. Evaluation of samples sintered between 1100° and 1220°C showed that densification proceeds rapidly for sintering temperatures 1170°C; for these specimens the room temperature resistivity increases to an equilibrium value with sintering time. Samples sintered to 99+% of theoretical density at lower temperatures densify slowly; the resistivity is invariant with sintering time. The Seebeck coefficient for the p -type ferrites is 550 μV/°C from 200° to 700°C; the dielectric constant varies from 17.3 at 0.5 MHz to 16.4 at 15 MHz.