Low Temperature Sintering Characteristics of Hot Press Sintered SrFe12O19 Ferrites for Use in Microwave LTCC Circulators

The SrFe12O19 ferrites with different amounts of Bi2O3 additive were prepared by a hot press sintering process at a low fired temperature of 870 °C in order to be compatible to the LTCC (low temperature co-fired ceramics) technology, and their low temperature sintering characteristics were investigated, including the crystal phase composition, sintering density, porosity, and magnetic properties. Results show that the addition of Bi2O3 promotes the formation of SrFe12O19 phase structure and increases the sintering compactness and magnetic properties of the ferrites fabricated at 870 °C. The ferrites with Bi2O3 content from 2 wt% to 4 wt% exhibit a compact microstructure with sintering density higher than 4.65 g·cm−3 and porosity lower than 10%, which contributes to the enhanced saturation magnetization Ms and intrinsic coercivity Hci above 252.4 kA·m−1 and 312.9 kA·m−1, respectively. Moreover, the potentiality of the SrFe12O19 ferrites for use in microwave LTCC circulators was also discussed based on their low temperature sintering characteristics.