Synthesis, microstructure, and dielectric properties of novel dual-phase high-entropy (Ba0.2Ca0.2Sr0.2Na0.2Bi0.2)WO4 ceramics for LTCC applications

Novel dual-phase high-entropy (Ba0.2Sr0.2Ca0.2Na0.2Bi0.2)WO4 ceramics were designed to reduce the sintering temperature and optimize the frequencytemperature coefficients of scheelite-type AWO4 ceramics. XRD and Rietveld refinement analyses revealed that the ceramic contained dual phases of BaWO4 and Na0.5Bi0.5WO4. The phases had a tetragonal structure with the I41/a space group, as verified by TEM. With increasing sintering temperature, the ɛr exhibited a decreasing trend owing to the combined influence of ionic polarizability and density. In addition, the variation trend of the Q × f value was similar to that of the density, and its intrinsic influence was investigated by analyzing the FWHM of the Raman vibrational peak. The τf was well optimized and exhibited a variation trend similar to those of the lattice distortion and microstrain. Finally, the (Ba0.2Sr0.2Ca0.2Na0.2Bi0.2)WO4 sintered at 950 °C had the outstanding properties: ɛr of 13.8, Q×f of 33,110 GHz and τf of −34 ppm/°C at 9 GHz.