Characterization and dielectric behavior of a new dielectric ceramics Ca(Mg_1/3Nb_2/3)O₃-(Ca_0.8Sr_0.2)TiO₃ at microwave frequencies

The crystal structures, phase compositions and the microwave dielectric properties of the (1-x)Ca(Mg_1/3Nb_2/3)O₃-x(Ca_0.8Sr_0.2)TiO₃ perovskite-based composites prepared by the conventional solid state route have been investigated. The formation of solid solution is confirmed by the XRD patterns. A rapid grain growth is observed at temperatures higher than 1470 °C, which would lead to a decrease in the density and Q × f of the ceramics. The temperature coefficient of resonant frequency increases with increasing (Ca_0.8Sr_0.2)TiO₃ content and tunes through near zero at x = 0.3. Specimen using 0.7Ca(Mg_1/3Nb_2/3)O₃-0.3(Ca_0.8Sr_0.2)TiO₃ possesses an excellent combination of microwave dielectric properties: ε_r ∼ 43.75, Q × f ∼ 45,200 GHz (where f = 6.3 GHz is the resonant frequency) and τ_f ∼ -4.2 ppm/°C. It is proposed as a suitable candidate material for small-sized GPS patch antennas.