Phase transitions and microwave dielectric properties of Bi3NbO7 ceramics with Bi4B2O9 addition

The effects of Bi4B2O9 on the phase transitions, sinterability and microwave dielectric properties of Bi3NbO7 ceramics were investigated. Densities around 96% theoretical could be achieved at 900 °C for samples with up to 20 wt% Bi4B2O9 addition. Phase transitions of cubic→tetragonal→cubic with the increase of sintering temperature were observed for the samples with Bi4B2O9 addition. Moreover, the Bi4B2O9 addition effectively accelerated the phase transition from cubic Bi3NbO7 to tetragonal Bi3NbO7. Bi4B2O9 addition and the sintering temperature significantly affected the microwave dielectric properties mainly due to the phase transitions. When 20 wt% Bi4B2O9 was added, a dense ceramic could be sintered at 900 °C with relative permittivity εr=79, microwave quality factor Qf0=1010 GHz, and temperature coefficient of resonance frequency τf=+8 ppm/°C, which makes it a promising candidate for LTCC applications.