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

The effects of the additives Bi
2
O
3
and Nb
2
O
5
on 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 Bi
2
O
3
enhances the sintering by forming a liquid phase in the ferrites, The additive Nb
2
O
5
enhances the sintering by increasing bulk diffusion due to the increased vacancy concentration which is accompanied by the solubility of Nb
⁵⁺
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, Nb
2
O
5
still leaves defects in the grains but Bi
2
O
3
does not. Thus the μQ product of Ni-Zn ferrites increases when the right amount of Bi
2
O
3
is added and decreases when Nb
2
O
5
is added. On the other hand, the square-loop properties of the lithium ferrites improve when the right amount of Nb
2
O
5
is added and degrade when Bi
2
O
3
is added.