Microwave dielectric properties of ZnAl2O4–TiO2 spinel-based composites

The microstructures, phase compositions and microwave dielectric properties of ZnAl2O4–TiO2 spinel-based composites have been investigated. It is found that ZnAl2O4 cannot form a solid solution with TiO2. As TiO2 content increases, the εr and τf values increase gradually, while the Q · f values degrade by degrees. Under the same amount of TiO2 content, the εr and Q · f values increase initially and then decrease slightly with increasing sintering temperature, while the τf values increase slowly. The optimal microwave dielectric properties are achieved in (1 − x)ZnAl2O4–xTiO2 (x = 0.21) sintered at 1500 °C for 3 h with εr value of 11.4, Q · f value of 71,810 GHz (at about 6.5 GHz), and τf value of − 0.5 ppm/°C.