Grain growth, densification and magnetic properties of NiZn ferrites with Bi₂O₃additive

Abstract

The grain growth, densification and magnetic properties of Bi2O3 doped NiZn ferrites prepared by a solid-state reaction method were investigated. Addition of a moderate content of Bi2O3 additive, to NiZn ferrite, due to its liquid phase sintering enhanced the diffraction intensity while excessive content of Bi2O3 produced a thick liquid phase layer at the grain boundaries and retarded mass transfer during sintering. Thus the x-ray diffraction peaks exhibited reduced intensity. In samples with higher additive content, Bi2O3 segregated at the grain boundaries as a liquid phase layer. This phenomenon could be confirmed by backscattering electron image. The grain growth of Bi2O3 doped NiZn ferrites was discussed by using the liquid phase sintering mechanism. Bi2O3 promoted grain growth via liquid phase sintering, and the addition of the optimum content of Bi2O3 could enhance the density of the sample and reduce its porosity. The NiZn ferrite samples containing x = 0.20, 0.08 and 0.04 sintered at 1180 °C, 1220 °C and 1250 °C, respectively, exhibited high permeability (μi) and low core losses (PL) at 50 kHz and 150 mT. The losses here were composed mainly of hysteresis loss, both eddy current loss and residual loss were ignored. The addition of proper content of Bi2O3 can improve the saturation induction (Bs) and reduce the coercivity (Hc) by liquid phase sintering.