Microwave dielectric properties of Mg4Nb2O9 ceramics produced by hydrothermal synthesis

Mg4Nb2O9 ceramics have been prepared by a hydrothermal synthesis in order to reduce the sintering temperature. The sintering and microwave dielectric properties of the hydrothermally processed Mg4Nb2O9 were studied under various sintering temperatures ranging from 900 to 1300°C. The highest Q×fo value of 26,069 GHz was obtained at the sintering temperature of 1300°C and is attributed to the increased density and appropriate grain growth. τf value of −17.1 ppm/°C was improved by the addition of TiO2 and τf value of 6.7 ppm/°C was obtained at 20 wt% TiO2. Chemical compatibility of Mg4Nb2O9 with Ag was tested to identity the possibility of using Mg4Nb2O9 for an LTCC application. Since any secondary phase was not observed in the XRD pattern of the mixtures of Mg4Nb2O9 and Ag powder heat treated at 900°C, it was considered that the Mg4Nb2O9 system is applicable to the multilayer microwave devices using Ag as an electrode.