Microwave dielectric properties and microstructures of Ba2Ti9O20-based ceramics with 3ZnO–B2O3 addition

Microwave dielectric properties of the Ba2Ti9O20-based ceramics with ZnBO addition up to 3 wt.% and containing ZrO2 were investigated at the sintering temperatures ranging from 900 to 960 °C. Effects of the ZnBO addition on the bulk density, microstructure, and dielectric properties of the Ba2Ti9O20-based ceramics at microwave frequency were elucidated. X-ray diffraction (XRD) results show the presence of five crystalline phases, Ba2Ti9O20, BaZr(BO3)2, BaTi4O9, BaZrO3 and Zn2SiO4 in the sintered ceramics, depending upon the amount of ZnBO addition. Optimum dielectric properties were obtained for the Ba2Ti9O20-based ceramic with 1 wt.% ZnBO addition and sintered in air at 940 °C for 2 h, having the dielectric properties: Q = 1137 (Q × f = 8300), ɛr value = 27.3, and τf = 2.5 ppm/°C. In addition, to understand well the effect of the BaZr(BO3)2 phase on the dielectric properties of Ba2Ti9O20-based ceramics, the BaZr(BO3)2 composition was synthesised from individual BaCO3, ZrO2 and B2O3 powders. Plots of dielectric loss versus sintering temperatures show a linearity, and ranges from 0.85 (at 1080 °C) to 0.08 (at 1250 °C). However, the dielectric constant does not increase with increasing sintering temperature, and its value is maintained at 11–13.