Low-temperature sintering of Z-type hexagonal ferrite by addition of fluorine containing glass powder

Abstract

In order to reduce the sintering temperature of Ba₃Co₂Fe₂₄O₄₁ (Co₂Z), fluorine containing glass powder was added as a sintering aid to ferrite powder with a Co₂Z stoichiometric composition prepared by a solid-state reaction, and dense sintered specimens could be obtained at 1000°C in air. The densification was achieved by liquid-phase sintering which was induced by the melting of the additive glass at ∼800°C. The main crystalline phase was Co₂Z, and spinel ferrite appeared as the impurity phase. By sintering in a sealed container, the densification was accelerated still more, and in addition to spinel ferrite, Ba-M also appeared as the impurity phase. The Ba-M contained some Co instead of Fe, and grew to discontinuously large hexagonal plate-like grains. In a fluorine and/or fluorides rich atmosphere, Co₂Z was discomposed to Ba-M and spinel ferrite, and large hexagonal plate-like grains appeared. These results suggest that fluorine and/or fluorides evaporated from the additive glass decomposed Co₂Z to Ba-M and spinel ferrite, and induced the discontinuously grain growth of Ba-M. The initial permeability was lower than that of the specimen with no additive glass but remained almost constant in the frequency regions up to 1 GHz.