Synthesis and microwave dielectric properties of pseudobrookite-type structure Mg5Nb4O15 ceramics by aqueous sol–gel technique

Pseudobrookite-type Mg5Nb4O15 ceramics were prepared by aqueous sol–gel process and microwave dielectric properties were investigated. Highly reactive nanosized Mg5Nb4O15 powders were successfully synthesized at 600 °C in oxygen atmosphere with particle sizes of 20–40 nm firstly and then phase evolution was detected by DTA-TG and XRD. Sintering characteristics and microwave dielectric properties of Mg5Nb4O15 ceramics were studied at different temperatures ranging from 1200 °C to 1400 °C. With the increase of sintering temperature, density, ɛr and Q·f values increased, and then saturated at 1300 °C. Excellent microwave properties of ɛr ∼11.3, Q·f ∼43,300 GHz and τf ∼−58 ppm/°C, were obtained finally. The sintering temperature of Mg5Nb4O15 ceramics was significantly reduced by aqueous sol–gel process compared to conventional solid-state methods.