Low-loss and ultra-low temperature sintering microwave dielectrics of pure and Ag-modified K2Mg2(MoO4)3 ceramics

Novel K2-2xAg2xMg2(MoO4)3 (x = 0-0.09) ceramics were synthesized by conventional solid-state sintering method. Based on the X-ray diffraction (XRD) patterns, all samples were identified to belong to an orthorhombic structure with a space group of P212121(19). The pure phase K2Mg2(MoO4)3 specimen when sintered at 590 degrees C revealed the favorable microwave dielectric properties: er of 6.91, Qxf of 21,900 GHz and zf of-164 ppm/degrees C. The substitution of Ag+ for K+ in K2-2xAg2xMg2(MoO4)3 (x = 0.01-0.09) ceramics led to the more stable structure and dramatically enhanced the Qxf to a value of 54,900 GHz at 500 degrees C. The microwave dielectric properties were related to the relative density, microstructure, ionic polarization, lattice energy, packing fraction, and bond valence of the ceramics. It was suggested that for ultra-low temperature co-fired ceramic (ULTCC) applications, K1.86Ag0.14Mg2(MoO4)3 ceramic could be sintered at 500 degrees C, which revealed an excellent combination of mi-crowave dielectric properties (er =7.34, Qxf =54,900 GHz and zf =-156 ppm/degrees C) and good chemical compat-ibility with aluminum electrodes.