Effects of Bi2O3and Nb2O5on the magnetic properties of Ni -Zn ferrites and lithium ferrites

The effects of the additives Bi2O3and Nb2O5on the sintering behavior and magnetic properties of Ni-Zn ferrites and lithium ferrites have been investigated by examination of microstructure and by measurements of permeability, loss factor and hysteresis curve. The additive Bi2O3enhances the sintering by forming a liquid phase in the ferrites, The additive Nb2O5enhances the sintering by increasing bulk diffusion due to the increased vacancy concentration which is accompanied by the solubility of Nb⁵⁺in the ferrites. Both additives leave microvoids and secondary phase precipitates in the grains when the sintering temperature is high. When the sintering temperature is low and the grain boundary mobility is small, however, Nb2O5still leaves defects in the grains but Bi2O3does not. Thus the μQ product of Ni-Zn ferrites increases when the right amount of Bi2O3is added and decreases when Nb2O5is added. On the other hand, the square-loop properties of the lithium ferrites improve when the right amount of Nb2O5is added and degrade when Bi2O3is added.