Microwave dielectric properties of Ba2−xSm4+2/3xTi9O26 ceramics with zero temperature coefficient

Ba2−xSm4+2x/3Ti9O26 (x=0–0.3) was selected as the formula for BaO–Sm2O3–4.5TiO2 ceramics based on the structure formula of the tungsten–bronze-type structure. The microstructure and microwave dielectric properties of Ba2−xSm4+2x/3Ti9O26 and the relationships between them were investigated in this study. The microstructure of Ba2−xSm4+2x/3Ti9O26 ceramics consists of a uniform matrix of primary BaO–Sm2O3–4TiO2 and BaO–Sm2O3–5TiO2 with small amounts of dispersed second phase, TiO2 and Ba2Ti9O20. Excellent dielectric properties of εr=68–79, Q×f=11 000–12 500 GHz and good temperature stability at the resonant frequency (τf=0 ppm per °C) were obtained. The relationships between the microstructure, second phases and microwave dielectric properties were concerned. XRD patterns, energy dispersive X-ray spectrometer (EDS) analysis and scanning electron microscopy are also presented.