Effects of Bi doping on sintering and dielectric characteristics of Ba_6-3xLa_8+2x (Ti_0.95 Zr_0.05)₁₈O₅₄(x=2/3) ceramics

The sintering properties, microstructures and dielectric characteristics of Ba_6-3x(La_1-m Bi_m)_8+2x (Ti_0.95Zr_0.05)₁₈O₅₄ (x=2/3) microwave dielectric ceramics prepared by conventional solid-state route were studied. The results show that Bi³⁺ replaced La³⁺ into A₁ rhombic sites and a single-phase solid solution with tungstenbronze-like structure formed in the range of 0<m<0.4. When Bi³⁺ content exceeds this range, a second phase of La_0.176Bi_0.824O_1.5 appears in the solid solution. Bi doping can lower the sintering temperature of Ba_6-3x(La_1-m Bi_m)_8+2x (Ti_0.95 Zr_0.05)₁₈O₅₄(x=2/3) ceramics from 1400°C to 1300°C, while a significant improvement of dielectric constant is achieved. The temperature coefficient of resonant frequency (τ_f) decreases, and the quality factor (Q·f) rapidly decreases. When m=0.05, the optimal microwave dielectric characteristics are achieved as ε_r=88.63, Q·f=4395 GHz, τ_f=6.25×10^-6/°C.