The effects of the additives $Nb_2O_5$, $V_2O_5$ and $Bi_2O_3$ on the sintering behavior and magnetic properties of lithium ferrite have been investigated and compared with Ni-Zn ferrite.
Ferrite specimens in the form of toroid core with various additives were prepared by conventional method.
The results showed that Nb ion and V ion had a small solubility in the lithium ferrite and solubility of V ion is greater than Nb ion. The additions of $Nb_2O_5$, $V_2O_5$ and $Bi_2O_3$ lowered that sintering temperature. These enhancements were explained by forming a liquid phase for $V_2O_5$ and $Bi_2O_3$ which have a low melting temperature, and by increasing volume diffusion for $Nb_2O_5$ due to the increased vacancy concentration which is accompanied by the solubility of Nb ion in the ferrite. The square loop properties of lithium ferrite can be improved when the right amount of $Nb_2O_5$ is added and degraded when $V_2O_5$ and $Bi_2O_3$ is added. On the other hand the μQ product of Ni-Zn ferrite can be increased when the right amount of $Bi_2O_3$ is added and decreased when $Nb_2O_5$ is added. These results were explained by the defects in the grains.
To clarify the effects of $Nb_2O_5$ and $V_2O_5$ on the sintering behavior of lithium ferrite, nonstoichiometry was used by controlling the amount of $Fe_2O_3$. $Li_{0.5}Fe_{2.46}O_4$ ($Fe_2O_3$-deficit) and $Li_{0.5}Fe_{2.54}O_4$ ($Fe_2O_3$-excess) with various additives were prepared by conventional method.
The results showed that the sintering is enhanced by forming a liquid phase when the added amount of $V_2O_5$ is considerably large. When $Nb_2O_5$ and small amount of $V_2O_5$ is added, the enhanced sintering is not caused by increasing volume diffusion due to the increased vacancy concentration, but increasing the material transport near the grain boundary. By the measurement of the material loss of lithium ferrite on heat treatment at high temperature, the loss of $O_2$ is increased by the addition of $Nb_2O_5$ and $V_2O_5$.
The squareness of lithium ferrite is increased by the addition of $Nb_2O_5$, and $Fe_2O_3$-deficit composition.
