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

Abstract

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 °C revealed the favorable microwave dielectric properties: εr of 6.91, Q×f of 21,900 GHz and τf of −164 ppm/°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 Q×f to a value of 54,900 GHz at 500 °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 °C, which revealed an excellent combination of microwave dielectric properties (εr =7.34, Q×f =54,900 GHz and τf =–156 ppm/°C) and good chemical compatibility with aluminum electrodes.