Preparation, Low-Temperature Sintering And Electrical Properties Of BNT Microwave Dielectric Ceramics

With the development of microwave technology, dielectric resonators and filters with excellent properties which were made up of microwave dielectric ceramics are widely used in many fields, such as satellite communications, mobile phone, modern medicine, and so on. Thereby the study of microwave dielectric ceramic materials has abstracted much attention. The fundamental purpose of this thesis is to investigate the preparation technology, low temperature sintering behavior and microwave dielectric properties of Ba6-3xNd8+2xTi18O54(x=2/3,BNT) ceramics with tungsten bornze-type structure.BNT ceramics have a sintering temperature as high as 1350oC. The effects of different sintering aids and different preparation technologies on the electrical properties were investigated. The mixtures of CuO-B2O3 and CaO-B2O3-SiO2 were the main additives used as sintering aids. Both solid-state method and citrate sol-gel route were used for preparing ceramic powders. The principal experimental results can be concluded as follows:Firstly, BNT ceramics were prepared by conventional solid-state method. The XRD results show that BNT ceramics have tungsten bornze-type like structure. When using CuO-B2O3 as sintering aids, it can be seen that CuO-B2O3 co-doping has an effect on the densification behavior, microstructure and microwave dielectric properties of BNT ceramics. When the content of CuO-B2O3 is 3wt%, the BNT ceramics can be well sintered at 950 oC and exhibit the best densification behavior and microwave dielectirc properties as:εr=63,Q·f=5000GHz. Secondly, a combination of chemical route derived pure powders plus the addition of a small amount of sintering aids, CuO and B2O3 was employed to decrease the sintering temperature. For 5wt% CuO-B2O3 modified BNT samples, the overall properties ofεr=63, Q·f=5300GHz and sintering temperature 925 oC are acceptable for applications. At last, the CaO-B2O3-SiO2 glass-ceramic was added into the BNT ceramic as sintering aids for not only reducing the sintering temperature but keeping the microwave dielectric properties at a high level as well. CaO-B2O3-SiO2 glass-ceramic has a low melting temperature and some of them were crystallized to form ceramic phase after sintering. With 2wt% content of CaO-B2O3-SiO2, the BNT ceramics can be well sintered at 950oC and show a good microwave dielectric properties asεr=68,Q·f=7400GHz.