抄録
The microwave dielectric properties of Al2O3-TiO2 ceramics were studied. The large negative temperature coefficient of the resonant frequency (τf) of Al2O3 ceramics was improved by adding rutile (TiO2), which has a large positive τf. In order to achieve τf of nearly zero, the post annealing treatment is necessary for the dense Al2O3-TiO2 ceramics sintered at more than 1300°C, because Al2TiO5 secondary phase appears during sintering. The previous study reported that the post-annealing treatment decomposed Al2TiO5 into Al2O3 and TiO2. However, a brief post-annealing accompanied to reduction of Qf. This study tries to make clear influence of the annealing on the decomposition and the microstructure as well as the microwave dielectric properties. Particularly, we focus on effect of starting particle sizes of TiO2 on the annealing process. It was found that difference in the starting particle size affected both decomposition process and grain growth during annealing. In the case that the small starting particle size (0.05 μm), Al2TiO5 phase was lightly decomposed by post annealing treatment for one time. The grains gradually grew as time of the post annealing treatment, resulting in increase of Qf. In the case of the large starting particle size (0.5 μm), Al2TiO5 phase remained slightly by post annealing treatment for one time and the grain size maintained without grain growth. The residual Al2TiO5 might bring the reduction of Qf and the Qf values maintain overall by mean of no grain growth.
