Abstract:
Microwave dielectric properties of polycrystalline Ca5Ta2TiO12 ceramics have been tailored using different glass additives. Several glasses such as B2O3, SiO2, B2O3-SiO2, ZnO-B2O3, Al2O3-SiO2, Al2O3-B2O3-SiO2, BaO-B2O3-SiO2, MgO-B2O3-SiO2, ZnO-B2O3-SiO2, PbO-B2O3-SiO2, and 2MgO-Al2O3-5SiO(2) were added to calcined Ca5Ta2TiO12 powder in different weight percentages. Among these glasses, addition of 0.1 wt% of SiO2, Al2O3-SiO2, Al2O3-B2O3-SiO2, MgO-B2O3-SiO2, and 2MgO-Al2O3-5SiO(2) improved the microwave dielectric properties. Fluxing of Ca5Ta2TiO12 with 0.1 wt% of 2MgO-Al2O3-5SiO(2) glass has epsilon(r)=39, Q(u)xf > 40 000 at 5 GHz and tau(f)=+8 ppm/degrees C. Near-zero tau(f) was obtained with the addition of glasses like Al2O3-SiO2, Al2O3-B2O3-SiO2, MgO-B2O3-SiO2, and 2MgO-Al2O3-5SiO(2). Addition of all the glasses except BaO-B2O3-SiO2 reduced the tau(f) of Ca5Ta2TiO12 ceramics. Two weight percent glass addition to Ca5Ta2TiO12 ceramics reduced their sintering temperature down to 1450 degrees C from 1625 degrees C and tau(f) close to zero but deteriorated the epsilon(r) and unloaded quality factor. The effects of glass content on the structure and microstructure of Ca5Ta2TiO12 ceramics were studied by X-ray diffraction and scanning electron microscopic techniques.
