Controlled Temperature Coefficient of Resonant Frequency of Al2O3-TiO2 Ceramics by Annealing Treatment

The microwave dielectric properties of alumina (Al2O3) ceramics were studied. Our objective was to improve the large negative temperature coefficient of resonant frequency (τf = -60 ppm/°C) of Al2O3 ceramics by the adding rutile (TiO2) with a large positive τf (+450 ppm/°C). A near-zero τf (τf = +1.5 ppm/°C) with excellent microwave dielectric properties (Q·f = 117,000 GHz, ε r = 12.4) was obtained in 0.9Al2O3-0.1TiO2 ceramics sintered at 1350°C for 2 h, followed by annealing at 1000°C for 2 h in air.