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 CaB_2+xO_4+3x/2 (x = 0–0.6) ceramics was investigated. The bond ionicity and the lattice energy of CaB_2+xO_4+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. CaB_2.3O_4.45 ceramic sintered at 950 °C had excellent properties: ε_r = 6.03, Q×f = 37,962 GHz, and τ_f = −24.7 ppm/°C. The influence of TiO₂ on the microwave dielectric properties of CaB₂O₄ was investigated, 87 wt% CaB₂O₄ - 13 wt% TiO₂ ceramics sintered at 950 °C showed a zero τ_f value.