Sintering behavior and microwave dielectric properties of Ba6−3xNd8+2xTi18O54 (x = 2/3) ceramics coated by H3BO3-TEOS sol–gel

H3BO3–Si(OC2H5)4 sol–gel was prepared and added as the sintering aid for Ba6−3xNd8+2xTi18O54 (x = 2/3, BNT) ceramic. The sintering behavior, microstructures, phase structures, and microwave dielectric properties were studied. The liquid phase was formed during the sintering process, which accelerated the process of reagent conversion and the mass-transport among the BNT powders. The sintering temperature of BNT ceramic was lowered from 1460 to 1075 °C. The H3BO3-TEOS sol–gel existed in the form of glass pellets, whose sizes were tens of nanometers, uniformly distributed around the BNT grains. By this method, perfect microstructures with BNT grains uniformly distributed in the ceramic matrixes were obtained, that were beneficial to the microwave dielectric properties of BNT ceramics. A ceramic composite which could be sintered well at 1075 °C and showed good microwave dielectric properties of ɛr = 73.8, Qf = 8190 GHz and TCF = 47.2 ppm/°C was obtained when 2 wt.% H3BO3-TEOS sol–gel was added to the BNT ceramic. The mechanism for the low temperature sintering and the relationship between microwave dielectric properties and microstructures were discussed.