A novel microwave dielectric ceramic CaB2O4 with low dielectric constant

A novel microwave dielectric ceramic CaB2O4 with low dielectric constant was synthesized by the solid-state reaction method. The impact of diverse Ca/B ratios on the phase composition, microstructure and dielectric properties of CaB2+xO4+3x/2 (x = 0-0.6) ceramics was investigated. The bond ionicity and the lattice energy of CaB2+xO4+3x/2 ceramics were calculated by the P-V-L theory. The appropriate excess of boron facilitated the densification of CaB2O4 ceramics, resulting in the stable crystal structure and enhanced dielectric properties. CaB2.3O4.45 ceramic sintered at 950 degrees C had excellent properties: epsilon(r) = 6.03, Qxf = 37,962 GHz, and tau(f) = -24.7 ppm/degrees C. The influence of TiO2 on the microwave dielectric properties of CaB2O4 was investigated, 87 wt% CaB2O4 - 13 wt% TiO2 ceramics sintered at 950 degrees C showed a zero tau(f) value.