Effect of Mg/B ratio and Sr2+ substitution for Mg2+ on the sintering, phase composition and microwave dielectric properties of Mg3B2O6 ceramics

Mg3B2O6 is a typical microwave dielectric ceramic with a high Qf value, but the pure Mg3B2O6 ceramic is difficult to be obtained due to the volatilization of B2O3 resulting from the high temperature during the fabrication process. We reveal the effects of Mg/B ratio and Sr2+ substitution for Mg2+ on the phase composition, sintering behavior, microstructure, and microwave dielectric properties of Mg3B2O6. The pure Mg3B2O6 ceramic can be obtained with Mg/B ratio equal to 1.2. Proper excessive free-MgO is benefit to the improvement of Qf value of Mg3B2O6, while it is detrimental to the densification of Mg3B2O6. No second phase was detected in the Sr2+ substituted Mg3B2O6 and excellent microwave dielectric properties (epsilon(r) = 6.9, Qf = 110820 GHz, and tau(f) = -32.4 ppm/degrees C at 12.8 GHz) were obtained in the (Mg0.998Sr0.002)(3)B2O6 (x = 0.2 mol.%) ceramic sample sintered at 1250 degrees C for 3h, making it a hopeful candidate for wireless communications. These results bring forward the underlying insights needed to direct the design of microwave dielectric ceramics with high Qf values for personal communication applications.