Dielectric properties and mixture behavior of Mg4Nb2O9-SrTiO3 ceramic system at microwave frequency

The microwave dielectric properties and the microstructures of the (1-x)Mg4Nb2O9-xSrTiO(3) ceramic system prepared by the conventional solid-state route were investigated. SrTiO3 was employed as a tau(f) compensator and was added to Mg4Nb2O9 to achieve a temperature-stable material. Corundum-structured Mg4Nb2O9 and perovskite-structured SrTiO3 were coexisted and the two-phase system was confirmed by the XRD and EDX analysis. Dielectric properties are correlated to the sintering temperature and the compositional ratio of the specimens. Although the E, of the specimen could be boosted by increasing amount of SrTiO3, it would instead render a decrease in the Q x f. The tau(f) value is strongly correlated to the compositions and can be controlled through the existing phases. In fact, tau(f) could be adjusted to near-zero by mixing 60 mole% Mg4Nb2O9 and 40 mole% SrTiO3. A dielectric constant (epsilon(r)) of 21.02, a high Q x f value of 112,000 GHz (measured at 9.7 GHz) and a temperature coefficient of resonant frequency (tau(f)) of 1.6 ppm/degrees C were obtained for 0.6Mg(4)Nb(2)O(9)-0.4SrTiO(3) sintered at 1300 degrees C for 4 h. It is proposed as a very promising dielectric material for low-loss microwave and millimeter wave applications. (C) 2008 Elsevier B.V. All rights reserved.