Effect of B₂O₃ additives on sintering and microwave dielectric behaviors of CuO-doped ZnNb₂O₆ ceramics

The influences of B₂O₃ additives on the sintering behavior and microwave dielectric properties of CuO-doped ZnNb₂O₆ ceramics were investigated. The B₂O₃ and CuO additives effectively lowered the sintering temperature of ZnNb₂O₆ ceramics to below 800°C. The sintering temperature of CaO-doped ZnNb₂O₆ decreased with increasing B₂O₃ content. Dielectric constant ε_r was not significantly changed and increased slightly with increasing B₂O₃ content, while the unloaded Q value was affected by the additives. The Q × f value was found to be a function of both the sintering temperature and the amount of additives. With 5 wt% CuO and 4wt% B₂O₃ additions, the Q × f value varied from 24000 to 46800 GHz as the sintering temperature increased from 780°C to 900°C for 2h. The τ_f value increased in positive values with B₂O₃ doped, while decreased in negative values with CuO addition. Zero temperature coefficient of the resonant frequency can be achieved by properly adjusting the concentration of additives. For low-firing multilayer applications, dielectric properties of ε_r ∼ 23.3, Q × f ∼ 46800 GHz and τ_f ∼ -6.7 ppm/°C can be obtained for doped ZnNb₂O₆ ceramics sintered at 900°C for 2 h.