Aluminum nitride(Al N) ceramics prepared by a fast spark plasma sintering method were heat-treated by a vacuum pressureless sintering method. Effect of sintering additive on the phase composition, microstructure, thermal and dielectric properties of Al N ceramics during high-temperature heat treatment process was investigated. The results show that the heat treatment enhances the growth of Al N grains and the distribution of secondary phases. Compared to Al N ceramics with single rare earth oxide, the therm...