Microstructure and dielectric properties of low temperature sintered ZnNb2O6 microwave ceramics

Abstract Low sintering temperature ZnNb 2 O 6 microwave ceramics were prepared by doping with mixed oxides of V 2 O 5 –Bi 2 O 3 and V 2 O 5 –Bi 2 O 3 –CuO. The effects of additives on the microstructure and dielectric properties of the ceramics were investigated. The results show that doping with V 2 O 5 –Bi 2 O 3 can reduce the sintering temperature of ZnNb 2 O 6 from 1150 °C to 1000 °C due to the formation of V 2 O 5 and Bi 2 O 3 based eutectic phases. The combined influence of V 2 O 5 and Bi 2 O 3 resulted in rod-like grains. Co-doping CuO with 1 wt.% V 2 O 5 –1 wt.% Bi 2 O 3 further lowered the sintering temperature to 880 °C, because eutectic phases could be formed between the CuO, V 2 O 5 and Bi 2 O 3 . A second phase of (Cu 2 Zn)Nb 2 O 8 also forms when the content of CuO is greater than 2.5 wt.%. A pure ZnNb 2 O 6 phase can be obtained when the amount of CuO was 1.0–2.5 wt.%. The Q × f values of ZnNb 2 O 6 ceramics doped with V 2 O 5 –Bi 2 O 3 –CuO were all higher than 25,000 GHz. The dielectric constants were 22.8–23.8 at microwave frequencies. In addition, the τ f values decreased towards negative as the content of CuO increased. The ceramic with composition of ZnNb 2 O 6 + 1 wt.%V 2 O 5 + 1 wt.% Bi 2 O 3 + 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 τ f is −44.89 ppm/°C, which makes it a promising material for low-temperature co-fired ceramics (LTCCs).