Ceramic Ni-Zn spinel have been prepared with iron varying from less than to more than the stoichiometric proportion, and thus with a wide range of resistives. Intergranular insulation has been achieved through penetration into the grain boundaries of an impregnation mixture (grain boundary barrier layer). Magnetic analyses, both thermomagnetic and high frequency, show that the impregnation has little, if any, effect on the grain composition. The frequency dependence of the permittivities reveals different behaviours varying with composition: samples with excess iron exhibit a dielectric relaxation in contrast to samples which are stoichiometric or deficient in iron. © 1990.
