Effects of Sm/Bi co-substitution on microstructures and microwave dielectric characteristics of Ba6−3xLa8+2xTi18O54 (x = 2/3) solid solution

Sm/Bi co-substitution for La in Ba6−3xLa8+2xTi18O54 (x=2/3) microwave dielectric ceramics was investigated. A single-phase solid solution with new tungsten bronze-type structure formed in the range of 0<z<0.2 for y=0.5 and 0<z<0.16 for y=0.7 in Ba6−3x(La1−y−zSmyBiz)8+2xTi18O54 ceramics. As Bi content exceeded these ranges, a secondary phase of Bi4Ti3O12 precipitated. Sm/Bi co-substitution significantly improved the temperature coefficient of resonant frequency (τf) and quality factor (Qf) in Ba6−3xLa8+2xTi18O54 ceramics, and good combinations of microwave dielectric properties were achieved: (1) ε=105, Qf=4,173 GHz, τf=−15 ppm/°C for y=0.7, z=0.12, and (2) ε=88.4, Qf=6,697 GHz, τf=+1 ppm/°C for y=0.7, z=0.04.