Study On The Preparation And Properties Of ZnO-Nb₂O5Based Microwave Dielectric Ceramics

In recently years, with the rapid development of microwave communicationtechnology, it has been strongly required that the related components based onmicrowave dielectric ceramics tend to miniaturization and integration. In order to meetthese requirements, design and fabrication of multilayer chip integrated circuitmicrowave components using low temperature co-fired ceramics technology hasattracted many attentions. From the view points of environmental protection andproduction cost cutting, microwave dielectric ceramics with excellent dielectricproperties and good compatibility with inner electrode such as Ag and Cu in co-firingwere required for low temperature co-firing ceramics applications. At present,lowering the sintering temperature of the microwave dielectric ceramics to co-fire withlow melting point of metal electrode is the hotspots in the materials research field.ZnO-Nb₂O₅system ceramics has excellent microwave dielectric properties. Thesintering temperature is only1200°C, so ZnO-Nb₂O₅based ceramics material becomesthe promising candidate for preparing multilayer chip and miniaturization microwavecomponents. Therefore, ZnO-Nb₂O₅system ceramics was selected as the investigateobjects in this dissertation. The ZnNb₂O₆ceramics powder was prepared by solidphase reaction method and the effects of presintering technics on microwave dielectricproperties of ZnNb₂O₆ceramics was investigated. TiO₂was introduced and its effecton microwave dielectric properties of ZnNb₂O₆ceramics was investigated. TheZnTiNb₂O₈ceramics powder was also prepared by two-step solid phase reactionmethod and the low temperature sintering research of ZnTiNb₂O₈ceramics wasinvestigated. The main research results are as follows:1. The synthesis of ZnNb₂O₆ceramics powder and the influence of presinteringtechnics on dielectric properties of ZnNb₂O₆ceramics.The pure phase ZnNb₂O₆ceramics powder can be synthesized at1000°C.Improved presintering temperature is helpful for the grain growth and grain with larger and uniform size were obtained. The optimum microwave dielectric properties ofεr=23.9, Q×f=76071GHz, τf=-60.9ppm/°C were obtained in ZnNb₂O₆ceramicssintered at1200°C for3h.2. The effects of TiO₂on microwave dielectric properties of ZnNb₂O₆ceramics.The phase composition of ZnNb₂O₆ceramics changed and the sinteringtemperature can be lowered to1150°C with the introduction of TiO₂powder. With theincreasing content of TiO₂, the dielectric constant increased gradually, the qualityfactor decreased, and the temperature coefficients of resonant frequency closed to zerogradually. The optimum microwave dielectric properties of εr=46.2, Q×f=48000GHz,τf=-8ppm/°C were obtained in ZnNb₂O₆-1.5TiO₂ceramics sintered at1150°C for3h.3. The synthesis of ZnTiNb₂O₈ceramics powder and the low temperaturesintering of ZnTiNb₂O₈ceramics.The ZnTiNb₂O₈ceramics powder was synthesized at1100°C for3h by two-stepsolid phase reaction method using ZnO, Nb₂O₅and TiO₂as raw materials. Thesintering temperature of ZnTiNb₂O₈ceramics can be lowered from1200°C to950°Cwith the introduction of Cu powder and its oxidation. The second phase was detectedin ZnTiNb₂O₈ceramics when the Cu powder content beyond3.0wt.%. The optimummicrowave dielectric properties of εr=30.2, Q×f=27537GHz, τf=-57.1ppm/°C wereobtained in the3.0wt.%Cu powder doped ZnTiNb₂O₈ceramics specimens sintered at950°C for3h.