Sintering behavior and microwave dielectric properties of nano alpha-alumina

The microstructures and the microwave dielectric properties of nano alpha alumina (α-Al2O3) 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 α-Al2O3 ceramics can be sintered at 1450 °C and increased beyond 99% of its theoretical density at 1500 °C. The specimens demonstrated single α-Al2O3 phase throughout the entire experiments. The dielectric constant (ɛr) and temperature coefficient of resonant frequency (τf) were not significantly affected, while the unloaded quality factors Q were effectively promoted at temperatures higher than 1450 °C. The ɛr value of 10, Q × f value of 521,000 (at 14 GHz) and τf value of − 48.9 ppm/°C were obtained for α-Al2O3 ceramics without sintering aid at 1550 °C for 4 h.