Synthesis of CaAl2xB2O4+3x: Novel microwave dielectric ceramics with low permittivity and low loss

Novel CaAl 2 x B 2 O 4+3 x ( x  = 0.25, 0.5, 0.75, and 1) ceramics were prepared via solid-state reaction method. The investigation is concentrated on sintering behavior, phase composition and dielectric properties of CaAl 2 x B 2 O 4+3 x ceramics with various ratios of Al 2 O 3 content. The optimal sintering temperature and the content of CaAl 2 B 2 O 7 are highly related to the variation of x value. CaAl 2 x B 2 O 4+3 x ceramics possess excellent microwave dielectric properties: ε r  = 5.8 ± 0.05, Q × f  = 63,338 ± 2690 GHz (@13.57 GHz), and τ f =-29 ± 2 ppm/℃ when sintered at 940 ℃ for x  = 0.5. Comparing the properties of CaAl 2 x B 2 O 4+3 x ceramics with reported borate ceramics, the ceramics prepared in this study with low dielectric loss and low sintering temperature have promising prospects in LTCC technology.