Ni-Cu-Zn Ferrites for Low Temperature Firing: I. Ferrite Composition and its Effect on Sintering Behavior and Permeability
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Ni-Cu-Zn ferrites of composition Ni1 − x − yCu y Zn x Fe2O4 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^∘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 μ = 500–1000 for x = 0.6. The Curie temperature is sensitive to composition and changes form about 150^∘C for x = 0.6 to T c > 250^∘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^∘C. The maximum shrinkage rate is shifted to T < 900∘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.
Keywordssoft ferrites Ni-Cu-Zn ferrites high permeability powder morphology
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