The effect of Ti/Ba ratio on the microstructures and microwave dielectric properties of BaTi4O9–Ba2Ti9O20 composite ceramics

Considering the strengths and weaknesses of the two distinct physical phases of BaTi4O9 and Ba2Ti9O20, we opted to combine them in order to harness the synergistic effects of their properties. In contrast to conventional two-phase composites, we synthesized BaTi4O9–Ba2Ti9O20 microwave ceramics with varying Ti/Ba ratios utilizing the solid-state reaction method. The phase compositions, surface morphologies, microwave dielectric properties and impedance analyses of the composite ceramics with different Ti/Ba ratios were systematically investigated. The X-ray diffractograms showed that the content of BaTi4O9 decreases rapidly as the Ti/Ba ratio increases from 4.15 to 4.35 and Ba2Ti9O20 becomes the main phase when Ti/Ba = 4.25. From complex impedance spectra, it can be seen that the arc gradually compresses as the Ti/Ba ratio increases, representing a decrease in the resistance. The ceramic possessing a Ti/Ba ratio of 4.15 exhibited superior microwave dielectric properties, characterized by Q × f = 16,622 GHz, εr = 38.01, and τf = 10.37 ppm/°C. These results provide guidance for the future design of high-performance microwave ceramics with medium dielectric constant.