Effect of ZnO ratio on sintering behavior and microwave dielectric properties of BaO–ZnO–TiO2 ceramics

Effect of ZnO ratio on the phase formation, the microstructure and microwave dielectric properties of BaO–ZnO–TiO2 ceramics with compositions varying from 1:0.5:3 to 1:0.8:3 (BaO:ZnO:TiO2) were investigated. XRD patterns show that the main crystal phase of the ceramics sintered at 1160 °C to 1220 °C for 2 h was Ba4ZnTi11O27, accompanied by a small number of additional phases: BaZn2.03Ti3.93O10.89 and Ba2ZnTi5O13, but note that all the ceramics with different ZnO ratio sintered at 1180 °C had pure Ba4ZnTi11O27 phase. SEM photographs suggest that ZnO working as sintering aids promoting the densification and grain growth, so when the proportion of ZnO was increased, the dielectric constant increased monotonically, τf values decreased continuously and Q × f values increased first and then declined. Ceramics with composition BaO–0.6ZnO–3TiO2 sintered at 1180 °C had compact and homogeneous microstructure and possessed excellent microwave dielectric properties: relative dielectric constant ɛr = 35.77, Q × f = 21,288 GHz and the temperature coefficient of resonant frequency τf = 1.25 ppm/°C.