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 Nb 2 O 5 and Bi 2 O 3 . The influence of Bi 2 O 3 additives on the microstructure and magnetic properties of NiCuZn ferrite, especially for grain growth and grain size, have been investigated. SEM results indicated that Nb 2 O 5 can obviously suppress grain growth when a small amount of Bi 2 O 3 was added. Also, the liquid phase of Bi 2 O 3 only can promote movement of grain boundary and reduce porosities between grains. Thus, a NiCuZn ferrite with high permeability ( μ i ′ = 472.79), high saturation flux density ( B s  = 0.313 T), high Q value (66.3) and low coercivity ( H c  = 94.75 A/m) was obtained when 0.25  wt % Nb 2 O 5 -0.50  wt % Bi 2 O 3 was added. It is proved that improvement of compactness can enhance magnetic properties even though grain growth was suppressed. However, over much Bi 2 O 3 (more than 1.00  wt %) reduced the magnetic properties due to deterioration of grains uniformity and existence of non-magnetic Bi 2 O 3 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.