Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO2 additives on the microstructure and microwave dielectric properties of Al2O3 ceramics were investigated. Al2O3 ceramics with CuO and TiO2 additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti4Cu2O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO2 content, due to the formation of the second phase Ti4Cu2O. However, the varying behaviors of the dielectric constant (ɛr) and temperature coefficients (τf) were associated with phase constitutions, as a result of the change of CuO and TiO2content. The τf can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO2. The specimens with 0.5 wt.% CuO and 7 wt.% TiO2 sintered at 1,360 °C for 4 h showed ɛr of 11.8, Qf value of 30,000 GHz, and τf of −7 ppm/°C.