Novel Bi2O3-added Al2Mo3O12 composite microwave dielectric ceramics for ULTCC applications

Abstract Ultra-low temperature co-fired ceramics (ULTCC) technology has been extensively developed in modern microwave communications, for which microwave dielectric ceramics with ultra-low sintering temperature play a crucial role. Among them, Al2Mo3O12 is a promising candidate with excellent microwave dielectric properties, but its sintering temperature (roughly 790 °C) is still too high for ULTCC. In this work, novel Bi2O3-added Al2Mo3O12 composite microwave dielectric ceramics were designed and prepared by conventional solid-state sintering reaction. The addition effects of Bi2O3 on the phase composition, microstructure and microwave dielectric properties of the obtained composite ceramics were investigated. The added Bi2O3 will react with Al2Mo3O12 to form a new Bi2Mo3O12 phase with an even lower melting point than Bi2O3, effectively reducing the sintering temperature of the composite ceramics to below 660 °C. As the extra addition amount of Bi2O3 increases from 0 to 5 wt%, for the composite ceramics sintered at the designed different temperatures (620–710 °C) for 12 h, the dielectric constant (er) increases from 5.5 to 5.98, quality factor (Q×f) could be effectively enhanced, reaching a maximum of 49900 GHz, and temperature coefficient of the resonant frequency (τf) changes from −36.4 to −42.8 ppm/oC. With 4 wt% Bi2O3, the composite ceramics sintered at 650 °C for 12 h present good microwave dielectric properties of er = 5.91, Q×f = 49600 GHz and τf = −41.2 ppm/oC, and excellent chemical stability with the electrode metal Al, indicating that it is a promising candidate for ULTCC applications.