Study On Low Temperature Sintering And Microwave Dielectric Properties Of7NiNb₂O₆-9TiO₂Ceramics

With the growing needs of electronic products with small size, light weight, morefunctions， and high integration, using LTCC （Low Temperature co-firing ceramic）technology to design and fabricate microwave components has become a research hotspot. Inorder to meet the requirement of reducing the size of the microwave components （such asdielectric resonator, frequency filter, oscillator, and so on）, choosing microwave dielectricmaterials with higher dielectric permittivity as the key materials is essential. Thus, the studyon low temperature sintering and microwave dielectric properties of ceramics with highdielectric permittivity means a lot to the production of small-sized and high-qualitymicrowave components.The pure7NiNb₂O₆-9TiO₂ceramics exhibit high dielectric permittivity of68.7, a Q×fof19300GHz, and acceptable Ï„fof56.6ppm/°C. But they show a high sintering temperature,which means can not be sintered with Ag （Cu） electrodes. So it is essential to lower itssintering temperature. In this paper, the effects of additives on sintering temperature andmicrowave dielectric properties of7NiNb₂O₆-9TiO₂ceramics have been investigated. Thephases and microstructure have been evaluated using X-ray diffraction （XRD） and scanningelectron microscopy （SEM）, and the microwave dielectric properties have been measured byAdvantest network analyzer.First, the mixture of CuO and H3BO3was used as the sintering aids to lower thesintering temperature of7NiNb₂O₆-9TiO₂ceramics, which prepared by solid-state reactionmethod. The results show that the mixture reduced the sintering temperature of7NiNb₂O₆-9TiO₂ceramics, but the effect is not enough （1000°C）. Moreover, it is observedthat the density of the specimen decreased with the increase of H3BO3content, but increasedwith the increase of CuO content.Then, the CuO was used as the sintering aids to lower the sintering temperature of7NiNb₂O₆-9TiO₂ceramics. The results show that the CuO-liquid phase exists in theboundary of grains, and the addition of CuO does not cause a secondary phase. The CuO canobviously promote the densification of7NiNb₂O₆-9TiO₂ceramics without decreasing the dielectric properties, and reduced its sintering temperature from1,200°C to935°C. The7NiNb₂O₆-9TiO₂ceramics with the addition of3.2wt.%CuO sintered at935°C affordedexcellent dielectric properties of εr=60.5, Q×f=10039GHz （at3.8GHz） and Ï„f=62ppm/°C. Moreover, stable microwave dielectric properties were obtained in7NiNb₂O₆-9TiO₂ceramics doped with3.2wt.%CuO sintered at the temperature from935°C to1005°C.