The influences of Fe2O3 additives on the sintering behavior and microwave dielectric properties of Mg4Nb2O9 ceramics were investigated. The prepared ceramics exhibits a mixture of phases Mg4Nb2O9 and Mg5Nb4O15. Lowering the sintering temperature (as low as 1240 °C) and promoting the Q × f value of Mg4Nb2O9 ceramics could be effectively achieved by adding Fe2O3 (up to 1 wt%). At 1270 °C, 0.75 wt% Fe2O3-doped Mg4Nb2O9 ceramics possess a dielectric constant (εr) of 13.46, a Q × f value of 280,000 GHz, and a temperature coefficient of resonant frequency (τf) of -62 ppm/°C. In contrast to that of pure Mg4Nb2O9 ceramics, incorporating additional Fe2O3 helps to render a dielectric material with a >40% dielectric loss reduction, a higher dielectric constant and retains a comparable τf, which makes it a very promising candidate for applications requiring an extremely low microwave dielectric loss.
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