Ni-Cu-Zn ferrites for low temperature firing:: I.: Ferrite composition and its effect on sintering behavior and permeability

Ni-Cu-Zn ferrites of composition Ni1-x-yCuyZnxFe2O4 with 0.4 <= x <= 0.6 and 0 <= y <= 0.25 were prepared by standard ceramic processing routes. The density of samples sintered at 900 degrees C increases with copper concentration y. Dilatometry reveals a significant decrease of the temperature of maximum shrinkage with y. The permeability has maximum values of mu = 500-1000 for x = 0.6. The Curie temperature is sensitive to composition and changes form about 150 degrees C for x = 0.6 to T-c > 250 degrees C for x = 0.4, almost independent on the Cu-content. A small iron deficiency in Ni0.20Cu0.20Zn0.60+zFe2-zO4-(z/2) with 0 <= z <= 0.06 significantly enhances the density of samples sintered at 900 degrees C. The maximum shrinkage rate is shifted to T < 900 degrees C. These compositions are therefore appropriate for application in low temperature co-firing processes. The permeability is reduced with z, hence a small z = 0.02 seems to be the optimum ferrite composition for high sintering activity and permeability.