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-Al 2O3 phase throughout the entire experiments. The dielectric constant (εr) 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 εr 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.
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