Effects of B₂O₃ Addition on the Microwave Dielectric Properties of Ba₂Ti₉O₂₀ Ceramics

Microwave characteristics of Ba₂Ti₉O₂₀ ceramics added with different amounts of B₂O₃ and sintered at high temperatures ranging from 900 to 960°C for 2 h are investigated. It is found that the firing temperature required to densify the Ba₂Ti₉O₂₀ ceramics is lowered by increasing the B₂O₃ content. The density and dielectric constants of the B₂O₃-added ceramics also increase with B₂O₃ addition. The results of X-ray diffraction (XRD) indicate the presence of five crystalline phases, Ba₂Ti₉O₂₀, BaZr(BO₃)₂, BaZrO₃, BaTi₄O₉, and Zn₃(BO₃)₂, in the sintered ceramics, depending upon the amount of B₂O₃ added. Optimum dielectric properties, i.e., Q=1477 (Q×f=10784), ε_r=28.3, and τ_f=-8.2, are obtained for the Ba₂Ti₉O₂₀ ceramics with 3 wt% B₂O₃ addition and sintering in air at 940°C for 2 h.