Effects of Bi2O3 addition on the microstructures and microwave dielectric characteristics of Ba6 − 3x(Sm0.2Nd0.8)8 + 2xTi18O54(x = 2 / 3) ceramics

The influences of Bi2O3 addition on the microstructures, phase structures and microwave dielectric properties of Ba6 − 3x(Sm0.2Nd0.8)8 + 2xTi18O54(x = 2 / 3) solid solution were studied. The Bi2O3-doped ceramics sintered under different conditions were characterized by X-ray diffraction spectra (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). It was found that Bi ions replaced Ba into the A2 pentagonal sites and a single-phase solid solution containing tungsten bronze-type like structure formed when Bi2O3 addition didn't exceed 1.0 wt.%. In 2.0 wt.% Bi2O3-doped Ba6 − 3x(Sm0.2Nd0.8)8 + 2xTi18O54(x = 2 / 3) solid solutions, a secondary phase of Ba2Ti9O20 precipitated. Bi2O3 addition not only significantly lowered the sintering temperature of the ceramics by approximately 130 °C, but also improved the dielectric constant (ε) and decreased the temperature coefficient of resonant frequency (τf). In addition, The quality factor (Q ▪ f) increased with increasing Bi2O3 addition until it reached the maximum value at 1.0 wt.% Bi2O3 addition. The optimal microwave dielectric properties were achieved with the Ba6 − 3x (Sm0.2Nd0.8)8 + 2xTi18O54(x = 2 / 3) ceramic doped with 1.0 wt.% Bi2O3 addition: a ε value of 82.1, a Q ▪ f value of 8537.6 (GHz) and a τf value of 17.3.