Effects of ZnO additive on crystalline phase and microwave dielectric properties of 0.90Al2O3–0.10TiO2 ceramics

0.90Al2O3–0.10TiO2 doped with x mol% ZnO (x = 0.2, 0.3, 0.4, 0.5) microwave dielectric ceramics, have been prepared by the conventional solid-state method with various sintering temperatures. A relationship between phase composition and microwave dielectric properties was systematically discussed for millimeter-wave applications. The formation of Al2TiO5 impurity phase was inhibited by ZnO addition without annealing treatment. The existence of Al2TiO5 impurity phase deteriorated seriously the microwave dielectric properties, especially quality factor (Q × f) and temperature coefficient (τf). Due to the liquid sintering effect, the addition of ZnO could reduce the sintering temperature to 1300 °C. To a large extend, ZnO additive improved the density of 0.90 Al2O3–0.10 TiO2 ceramics, and ultimately enhanced the microwave dielectric properties. The ZnAl2O4 impurity phase could also enhance the Q × f value and permittivity (εr) of 0.90Al2O3–0.10TiO2 ceramics. Excellent microwave dielectric properties was achieved for 0.4 mol% ZnO doped 0.90Al2O3–0.10TiO2 ceramics sintered at 1300 °C for 4 h: εr = 12.4, Q × f = 159,000 GHz, τf = −0.2 ppm/°C.