Microstructure and dielectric properties of low temperature sintered ZnNb2O6 microwave ceramics

Low sintering temperature ZnNb2O6 microwave ceramics were prepared by doping with mixed oxides of V2O5–Bi2O3 and V2O5–Bi2O3–CuO. The effects of additives on the microstructure and dielectric properties of the ceramics were investigated. The results show that doping with V2O5–Bi2O3 can reduce the sintering temperature of ZnNb2O6 from 1150 °C to 1000 °C due to the formation of V2O5 and Bi2O3 based eutectic phases. The combined influence of V2O5 and Bi2O3 resulted in rod-like grains. Co-doping CuO with 1 wt.% V2O5–1 wt.% Bi2O3 further lowered the sintering temperature to 880 °C, because eutectic phases could be formed between the CuO, V2O5 and Bi2O3. A second phase of (Cu2Zn)Nb2O8 also forms when the content of CuO is greater than 2.5 wt.%. A pure ZnNb2O6 phase can be obtained when the amount of CuO was 1.0–2.5 wt.%. The Q × f values of ZnNb2O6 ceramics doped with V2O5–Bi2O3–CuO were all higher than 25,000 GHz. The dielectric constants were 22.8–23.8 at microwave frequencies. In addition, theτf values decreased towards negative as the content of CuO increased. The ceramic with composition of ZnNb2O6 + 1 wt.%V2O5 + 1 wt.% Bi2O3 + 2.5 wt.% CuO sintered at 880 °C exhibited the optimum microwave dielectric properties, ɛ is 23.4, Q × f is 46,975 GHz, and τf is −44.89 ppm/°C, which makes it a promising material for low-temperature co-fired ceramics (LTCCs).