The effect of Fe2O3-LiF co-doping on the sintering behavior, phase compositions and microwave dielectric properties of Mg4Nb2O9-CaTiO3 ceramics were investigated. The Fe2O3-LiF addition effectively lowered the sintering temperature of Mg4Nb2O9-CaTiO3 ceramics from 1275 oC to 1025 oC. XRD showed the presence of LiFe5O8 and Ca(FeTi)2O4 as second phases. With an increase in the sintering temperature, the dielectric constant (εr) and quality factor (Q·f) first increase and decrease thereafter, the temperature coefficient of resonant frequency (τf) changes slightly. A Mg4Nb2O9-CaTiO3 specimen with 0.75wt% Fe2O3-1.5 wt%LiF sintered at 1025 oC/5 h exhibited good microwave dielectric properties: εr = 13.6, Q·f = 64 430 GHz (9.5 GHz) and τf = −60.4 ppm/K. These properties were correlated with the formation of the second phases, LiFe5O8 and Ca(FeTi)2O4.

Keywords: Dielectric ceramics, Dielectric properties, Sintering aids.