Tailoring the microwave dielectric properties of Ca5Ta2TiO12 ceramics through glass addition

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.