Sintering behavior and dielectric properties of SiO2-BPO4 glass-fluxed ceramics

(1-x)SiO2-xBPO4 (x = 23-70 wt%) glass-fluxed ceramics have been prepared by a traditional ceramic process. The phase assemblage, sintering, crystallization behavior, microwave dielectric properties and chemical compatibility with Ag/Cu have been studied. The SiO2-rich compositions (x = 23-50 wt%) could be well densified at ∼975 °C/2 h, while the BPO4-rich compositions demonstrated poor sinterability and porous microstructure. The SiO2-rich compositions sintered at 975 °C/2 h contained BPO4, low temperature cristobalite and glassy phases. Crystallization of BPO4 occurred at lower temperature than that of SiO2. Good combined microwave dielectric properties with Ɛr = ∼5, Q × f = 25,000 GHz and τf value of -7.3 ppm/°C could be obtained when 10 wt% TiO2 was added after sintering at 975 °C/2 h. The x = 23 wt% composition chemically reacted with Ag, but exhibited good chemical compatibility with Cu after sintering at 975 °C/2 h.