Microwave Dielectric Properties of Low Temperature Sintered Al₂O₃ Ceramics

With the rapid development of information and communication technology, microwave dielectric materials have also developed correspondingly. Al₂O₃ ceramics are widely used in resonators, ceramic substrates, and satellite communication devices due to their excellent microwave dielectric properties. However, the sintering temperature of Al₂O₃ ceramics is relatively high. Considering environmental protection, energy saving and emission reduction, low-temperature sintering of Al₂O₃ ceramics is also an important aspect which people pay attention to. Doping additives is a method that has been studied more and has a significant effect on reducing the sintering temperature of Al₂O₃ ceramics. Recently, CuO-TiO₂-Nb₂O₅ doping has attracted the attention of people because of its outstanding cooling effect. Although some reports show that it can effectively reduce the sintering temperature, and the Q×f value is low. The sintering behavior, microstructure and microwave dielectric properties of Al₂O₃ ceramics doped with 0.4%CuO-0.5%TiO₂-0.1%Nb₂O₅ are investigated. The results show that 0.4%CuO-0.5%TiO₂-0.1%Nb₂O₅ (mass fraction 1%) reduces the sintering temperature of Al₂O₃ ceramics effectively. Samples with relative densities higher than 96% and uniform microstructure can be obtained when sintered at 1150 ℃. Higher temperature can further increase the density of the samples, but it inevitably leads to abnormal grain growth. Meanwhile, the investigation results show that the low-firing Al₂O₃ ceramics have good microwave dielectric properties and especially high Q×f value. A high Q×f value of 64632 GHz could be obtained for the 1150 ℃ sintered sample. The reason for the low temperature densification, abnormal grain growth behavior and the changing trend of the microwave dielectric properties are discussed in the paper.