Microstructure and dielectric properties of Ba(Cd_1/3Ta_2/3)O₃ microwave ceramics synthesized with a boron oxide sintering aid

The use of boron as a sintering aid reduces the sintering temperature, enhances the sintering density, and improves the microwave properties of Ba(Cd_1/3Ta_2/3)O₃ ceramic dielectrics. Observations by transmission electron microscopy indicate that the liquid sintering mechanism contributes to the improvement in sintering density for boron concentrations exceeding 0.5 wt%. The introduction of as small as 0.01% boron also results in the production of high-density samples (∼95%), presumably indicating that a point defect mechanism may also play an important role in the sintering process. X-ray diffraction data combined with high-resolution transmission electron microscopy images show that boron-doped Ba(Cd_1/3Ta_2/3)O₃ ceramic material has a well-ordered hexagonal structure. Annealing treatment is found to improve the microwave properties. The best sample has a dielectric constant of 32, a temperature coefficient of resonant frequency of 80 ± 15 ppm/°C, and a quality factor of >25,000 at 2 GHz.