Structures and properties of LiBaF3 microwave dielectric ceramics for ULTCC applications

Perovskite structural LiBaF3 ceramics with excellent microwave dielectric properties were synthesized using traditional solid-state method. By regulating the sintering temperatures from 600 degrees C to 675 degrees C, LiBaF3 ceramics exhibit tunable dielectric constant (epsilon(r)) from 12.42 to 13.72, adjustable Q x f value from 55000 GHz to 73000 GHz, and regulable temperature coefficient of resonance frequency (tau(f)) from -36.78 ppm/degrees C to -34.68 ppm/degrees C. The properties are strongly associated with the density, and can be further optimized by 0.5 wt%TiO2 addition (epsilon(r) = 14.43, Q x f = 56000 GHz, tau(f) = -1.26 ppm/degrees C). The LiBaF3 ceramics also exhibit excellent compatibility with Ag and Al electrodes. Furthermore, relationships between multiscale structures and microwave dielectric properties of the ceramics were revealed. Oxidation behaviors between LiBaF3 and O-2 would result in the lattice shrinkage, the introduction of defect level, the decrease of bandgap and density, and then deteriorating the microwave dielectric properties. All the findings make the LiBaF3 ceramic a promising candidate for ULTCC application, and may facilitate the development of other novel microwave dielectric materials.