Microwave dielectric properties of low-fired CoNb2O6 ceramics with B2O3 addition

Low-fired B2O3-doped CoNb2O6 microwave dielectric ceramics were synthesized via conventional solid-state method. The effects of B2O3 additives on their sintering behavior, phase composition, and microwave dielectric properties were investigated systematically. The addition of B2O3 as liquid phase successfully lowered the sintering temperature of CoNb2O6 ceramics from 1200 to 1000 A degrees C. The system remained orthorhombic columbite phase at the level of 0.5-1.5 wt% B2O3 addition. However, a trace amount of Co4Nb2O9 second phase with major CoNb2O6 phase was observed for the 2 wt% B2O3-added sample. The microwave dielectric properties were found to strongly correlate with the sintering temperature as well as the amount of B2O3 addition. With 1.5 wt% B2O3, CoNb2O6 ceramics sintered at 1000 A degrees C possessed optimum microwave dielectric properties with an epsilon (r) of 22.4, a high Q x f of 43,979 GHz, and a tau (f) of -46.2 ppm/A degrees C.