Sintering behavior and microwave dielectric properties of nano alpha-alumina

摘要

The microstructures and the microwave dielectric properties of nano alpha alumina (alpha-Al_2O_3) ceramics have been investigated. It is found that the use of nano particle-sized starting material can significantly improve the densification and their microwave dielectric properties of the specimens. The alpha-Al_2O_3 ceramics can be sintered at 1450 deg C and increased beyond 99 percent of its theoretical density at 1500 deg C. The specimens demonstrated single alpha-Al_2O_3 phase throughout the entire experiments. The dielectric constant (epsilon_r) and temperature coefficient of resonant frequency (tau_f) were not significantly affected, while the unloaded quality factors Q were effectively promoted at temperatures higher than 1450 deg C. The epsilon_r value of 10, Q X f value of 521,000 (at 14 GHz) and tau_f value of -48.9 ppm/deg C were obtained for alpha-Al_2O_3 ceramics without sintering aid at 1550 deg C for 4 h.