Effects of CuO additives and sol–gel technique on NiNb₂O₆ dielectric ceramics for LTCC application

The effects of CuO additives and sol–gel method synthesis on the sintering behavior, microstructure and the microwave dielectric properties of NiNb₂O₆ ceramics were investigated systematically. The NiNb₂O₆ ceramics were synthesized with traditional solid state method and sol–gel method, and the CuO additives were used in the solid state method for comparison. The sintering temperature of NiNb₂O₆ ceramics with the highest densification can be effectively reduced from about 1275 °C to 1050 and 1100 °C respectively by using CuO additions and sol–gel technique. To study their applicability in low temperature co-fired ceramic technology, dielectric properties have been characterized. The dielectric properties exhibited a significant dependence on the sintering condition, composition and crystal structure of the ceramics. In particular, the 2.5 wt% CuO-doped NiNb₂O₆ ceramics sintered at 1050 °C have excellent microwave dielectric properties: ε_r = 21.45, Q × f = 23,531 GHz, τ_f = −27.9 ppm/°C. While the NiNb₂O₆ ceramics prepared by sol–gel method obtain microwave dielectric properties as: ε_r = 19.16, Q × f = 11,149 GHz, τ_f = −27.3 ppm/°C after sintered at 1100 °C for 2 h.