Microwave Dielectric Properties of Sintered Alumina Using Nano-Scaled Powders of α Alumina and TiO2

This chapter investigates the microstructure and the microwave dielectric properties of nano-scaled α alumina ceramics with various added amounts of nano-scaled TiO₂. The sintering temperature of nano-scaled α alumina can be effectively lowered by increasing the TiO₂ content. The Qxf values of nano-scaled α alumina could be tremendously boosted by adding an appropriate amount of TiO₂. However, introducing excessive TiO₂ into the alumina ceramics would instead lead to a decrease in the Qxf values. The phases of TiO₂ and Al₂Ti_O5 co-existed at 1350C, and the maximum Qxf value appeared right after the eradication of TiO₂ phase at 1400C. Consequently, increasing the TiO₂ content to 0.5 wt% yielded a Qxf value of 680000 GHz (measured at 14 GHz) for nano-scaled α alumina prepared at 1400C for duration of 4 h. Sintered ceramic samples were also characterized by X-ray diffraction and scanning electron microscopy.