Microstructure and dielectric properties of low temperature sintered ZnNb2O6 microwave ceramics
Introduction
Low-temperature co-fired ceramics (LTCCs) are interesting because of their application in novel multilayer communication modules involving microwave components. The major requirements for these materials are the ability to sinter below the Ag/Cu metallization melting temperature, chemical compatibility with the metallization material within the sintering process, and excellent microwave dielectric properties [1], [2]. Zinc niobite (ZnNb2O6) ceramic is one of the candidates for low-temperature sintering microwave dielectrics, with low sintering temperature (∼1150 °C) and promising microwave dielectric properties (Q × f = 87,300 GHz, ɛ = 25 and τf = −56 ppm/°C) [3], [4]. Although ZnNb2O6 ceramics have relatively low sintering temperature, it is still much higher than the melting points of Ag (961 °C) and Cu (1064 °C), which are used as the inner electrodes of LTCCs.
The use of low-melting additives such as glass or oxide is commonly used to reduce the sintering temperature of zinc niobite microwave ceramics [5], [6], [7]. V2O5, Bi2O3, and CuO are the low-melting oxides commonly used as sintering aids [8], [9], [10]. However, it has been found that doping with just one low-melting oxide additive does not lower the sintering temperature effectively, and doping glasses as sintering aids can result in the microwave dielectric properties deteriorating seriously. It is expected that ZnNb2O6 ceramics with multi-oxides additives V2O5, Bi2O3, and CuO may have excellent microwave properties combined with low sintering temperature [11]. The effects of multi-oxide additives on the sintering temperature and dielectric properties have seldom been reported.
In the present work, ZnNb2O6 based microwave dielectric ceramics were prepared by a conventional mixed-oxide method. V2O5–Bi2O3 and V2O5–Bi2O3–CuO multi-oxide additives were added to lower the sintering temperature. The effects of co-doping with the multi-oxide additives on the sintering temperature, microstructure and microwave dielectric properties of ZnNb2O6 ceramics were investigated.
Section snippets
Experimental
ZnNb2O6 based ceramics were prepared by the traditional solid-state method. The proportions of V2O5, Bi2O3 were 0.5–1 wt.%, and CuO was 0.4–5 wt.%, these were designated as BV1-4#, BVC1-4#, respectively, as shown in Table 1. Reagent pure ZnO, Nb2O5, V2O5, Bi2O3 and CuO were used as the starting materials. As the first step, equal moles of ZnO and Nb2O5 were ball-milled for 12 h. The mixture was then calcined at 1000 °C for 4 h to synthesize ZnNb2O6. Then stoichiometric quantities of ZnNb2O6, V2O5, Bi
Microstructure and dielectric properties of ZnNb2O6 ceramics co-doped with V2O5–Bi2O3
The density curves of the ZnNb2O6 ceramics doped with V2O5–Bi2O3 as a function of sintering temperature are shown in Fig. 1. It can be seen that the densities of the samples increased with increasing sintering temperature. The BV4# sample doped with 1 wt.% V2O5 and 1 wt.% Bi2O3 densified at 1000 °C, reaching 95% of the theoretical density. Over all, the densities of the ceramics increased steadily with increasing amounts of V2O5–Bi2O3. Therefore, V2O5–Bi2O3 additives are good for lowering the
Conclusions
Co-doping with 1.0 wt.%V2O5 and 1.0 wt.% Bi2O3 can lower the sintering temperature of ZnNb2O6 ceramics from 1150 °C to1000 °C, due to the eutectic phase formed by V2O5 and Bi2O3. Because of the co-effect of V2O5 and Bi2O3, there were rod-like and equiaxial grains coexisting in the ZnNb2O6 ceramics. Co-doping with CuO and V2O5–Bi2O3 can lower the sintering temperature of ZnNb2O6 ceramics even further. When the amount of CuO was more than 1.0 wt.%, the sintering temperature of ZnNb2O6 ceramics
Acknowledgments
This work was supported by Natural Science Foundation of Shanxi Province in China, Science and Technology Innovation Fund of Northwestern Polytechnical University.
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