Microstructure and dielectric properties control of Ba4(Nd0.7Sm0.3)9.33Ti18O54 microwave ceramics

Microwave ceramics of Ba4(Nd0.7Sm0.3)9.33Ti18O54 with 0–3 wt% Ag additions were synthesized by a citrate sol–gel method. The BaO–B2O3–SiO2 glass was also added into the sol–gel derived BNST ceramic powders as sintering aids. The undoped, Ag- and BaBS-doped samples can be sintered at 1250 °C, 1150 °C and 1000 °C, respectively. The microstructure and dielectric properties were then controlled by doping Ag or BaBS glass. Near isoaxial grains with about 250 nm and typical columnar grains were obtained for the silver-doped and BaBS-doped samples, respectively. For the <1 wt% silver-doped samples, the dielectric constant and Q × f retained unaltered but τf decreased from 9 ppm/°C to 1.4 ppm/°C. With increasing silver content from 1 wt% to 3 wt%, the dielectric constant and τf significantly increased but Q × f decreased. For the BaBS-doped samples, both dielectric constant and Q × f decreased but τf increased with increasing BaBS content.