Synthesis of low-temperature sintered M-type barium ferrites with enhanced microstructure, magnetic and dielectric properties

Abstract

M-type barium ferrites (BaM) are utilized in the preparation of ferrite circulators due to their excellent magnetic properties. However, high sintering temperature of BaM is one of the major problems unsuitable for actual production requirements. In this study, Bi3+ ions from the low-melting point oxide bismuth(III) oxide (Bi2O3) were made to substitute Fe3+ ions to reduce the sintering temperature and control the magnetic properties. Addition of an appropriate content of Bi3+ ions at the sintering temperature of 900 °C led to the disappearance of the second phase, and a pure BaBix(CoTi)1.2Fe9.6−xO19 phase was formed. The results exhibited the existence of dense microstructure in BaM ceramics. Moreover, when the x value of Bi2O3 was 0.45, the permeability of the sample increased from 12.59 to 21.6 at 10 MHz, the saturation magnetization reached 3313.34 gauss, and the permittivity increased from 10.75 to 21.24. Permeability and permittivity were found to be approximately equal. Interestingly, addition of excessive Bi2O3 led to the formation of the second phase, and the microstructure exhibited the appearance of abnormal grains. However, BaM still maintained acceptable magnetic properties. The results showed that the addition of Bi3+ ions could reduce the sintering temperature of the ferrite and simultaneously adjust the magnetic and dielectric properties. Therefore, this material may have good performance in the preparation of ferrite circulators.