Dielectric and thermal properties of AlN ceramics

The effects of slow-cooling and annealing conditions on dielectric loss, thermal conductivity and microstructure of AlN ceramics were investigated. Y2O3 from 0.5 to 1.25 mol% at 0.25% increments was added as a sintering additive to AlN powder and pressureless sintering was carried out at 1900 °C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 °C min−1 from 1900 to 1750 °C, subsequently cooled to 970 °C at a rate of 10 °C min−1 and then annealed at the same temperature for 4 h. AlN and YAG (5Al2O3/3Y2O3) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y2O3 had a low loss of <2.0 × 10−3 and a high thermal conductivity of >160 W m−1 °C−1.