Fundamentals of the densification mechanism of nicuzn-ferrites

Abstract

The partial substitution of Ni with Cu in NiZn-ferrites has many economical advantages in bulk magnetic component manufacturing and additional densification advantages in multilayer chip inductor manufacturing. However, the detailed mechanism through which the presence of Cu influences the densification of NiZn-ferrites has not been outlined in literature. In this article the mechanism of NiCuZn-densification has been explained on basis of point defect chemistry and changes in the type of major defects that dominate ion transport through sintering. Although the densification of NiZn-ferrites is mainly dictated by the Fe content and is restricted at Fe excess, in the presence of Cu this limitation does not hold any more because of the additional anion vacancies introduced due to Cu2+ to Cu+ reduction at elevated temperatures. In addition, further Cu reduction, through the usage of reductive atmospheres, enhances the densification even further and this provides an extra processing parameter for tuning densification. There is no evidence for liquid phase sintering due to the formation of liquid phases ought to the presence of Cu or associated eutectic mixtures.