Microwave Dielectric Properties of Ba_6-3xSm_8+2xTi₁₈O₅₄ (x=2/3) Ceramics Produced by Spark Plasma Sintering

Ba_6-3xSm_8+2xTi₁₈O₅₄ (x=2/3) microwave dielectric ceramics with a tungstenbronze-type like structure were synthesized by a spark plasma sintering (SPS) technique. Sintering was conducted under vacuum at temperatures ranging from 1100°C to 1200°C under 60 MPa. The microstructure and phase identification were analyzed by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD), respectively. The density of the sintered ceramics increased with an increase in temperature. Specimens with a density 98% of the theoretical density could be attained by sintering at 1200°C for 5 min with a heating rate of 200°C/min. Only a tungstenbronze-type like phase was identified in ceramics sintered at temperatures above 1100°C. Microwave dielectric properties also increased with sintering temperature, the sample sintered at 1200°C for 5 min exhibited superior microwave dielectric properties, such as dielectric constant ε_r=81.2, quality factor Q×f=10099 GHz and temperature coefficient τ_f=-17.2 ppm /°C. The results indicated that this technique was an alternative sintering method for synthesizing dense microwave dielectric ceramics at a rather low temperature and in a short time.