Densification and magnetic properties of NiCuZn low-sintering temperature ferrites with Bi2O3-Nb2O5 composite additives

Abstract

NiCuZn ferrite ceramics with high permeability and low magnetic loss have great values in high frequency applications. Here, we synthesized uniform and compact NiCuZn ferrites with small grains (about 1.5 μm) at 875 °C via adjusting additive amount of Nb2O5 and Bi2O3. The influence of Bi2O3 additives on the microstructure and magnetic properties of NiCuZn ferrite, especially for grain growth and grain size, have been investigated. SEM results indicated that Nb2O5 can obviously suppress grain growth when a small amount of Bi2O3 was added. Also, the liquid phase of Bi2O3 only can promote movement of grain boundary and reduce porosities between grains. Thus, a NiCuZn ferrite with high permeability (μi′ = 472.79), high saturation flux density (Bs = 0.313 T), high Q value (66.3) and low coercivity (Hc = 94.75 A/m) was obtained when 0.25 wt % Nb2O5-0.50 wt % Bi2O3 was added. It is proved that improvement of compactness can enhance magnetic properties even though grain growth was suppressed. However, over much Bi2O3 (more than 1.00 wt %) reduced the magnetic properties due to deterioration of grains uniformity and existence of non-magnetic Bi2O3 liquid phase. Such a low temperature solid phase synthesis method (i.e., adding composite additive with different melting point oxide) should also facilitate preparation of other advanced ceramics for practical applications.