Low-fired fluoride microwave dielectric ceramics with low dielectric loss

Low-fired fluoride microwave dielectric ceramics (LiF, CaF2, SrF2 and BaF2) were prepared through a simple one-step sintering process. Fluoride ceramics, especially LiF, which had the lowest sintering temperature of 800 °C, could be well sintered below 1050 °C. Rietveld refinement results showed that LiF, CaF2, SrF2 and BaF2 ceramics crystallized into a cubic structure with space group Fm-3m. The relative permittivity (εr), quality factor (Q × f) and temperature coefficient of the resonant frequency (τf) of the fluoride ceramics were closely related to relative density, the ionic polarizability of the primitive unit cell, the packing fraction and the bond valence. In this series of low-permittivity fluoride ceramics, LiF, CaF2 and BaF2 could be co-fired with Ag powders, and LiF ceramic exhibited the highest Q×f value of 73880 GHz, which is comparable to those of traditional oxide microwave dielectric ceramics.