Low-loss microwave dielectrics of Li_2(1–x)M_xWO₄ (M= Mg, Zn; x= 0.01–0.09) for ULTCC applications

Li_2(1–x)M_xWO₄ (M = Mg, Zn; x = 0.01–0.09) ceramics with an ultra-low sintering temperature of 540 °C were prepared by solid-state synthesis and their structural characteristics and microwave dielectric properties were systematically investigated. By replacing Li with 0.05 mol% Mg or 0.07 mol% Zn, the sintering temperature of the Li₂WO₄ dielectric could be brought down from 660 to 540 °C along with the combined dielectric properties of the ε_r of 6.2 and 5.8, a Q × f of 76,000 and 68,000 GHz, and the τ_f of −94 and −86 ppm/°C, respectively. The corrected dielectric constant was found to be proportional to the ratio of α_D(dielectric polarizability)/V_m(molecular volume). The results showed that the Q × f values could be dramatically improved by increasing the density, packing fraction and lattice energy. Moreover, the τ_f values of ceramics render a similar variation tendency by shifting linearly toward zero as the V_cation increases. The Li_2(1–x)M_xWO₄ ceramic is a glass-free, phase pure, and energy-saving dielectric ideal for ULTCC applications.