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 degrees C for 2 h in a nitrogen flowing atmosphere. To improve the properties, AlN samples were slow-cooled at a rate of 1 degrees C min(-1) from 1900 to 1750 degrees C, subsequently cooled to 970 degrees C at a rate of 10 degrees C min(-1) and then annealed at the same temperature for 4 h. AlN and YAG (5Al(2)O(3)/3Y(2)O(3)) were the only identified phases from XRD. AlN doped with 0.5 and 0.75 mol% Y2O3 had a low loss of < 2.0 x 10(-3) and a high thermal conductivity of > 160 W m(-1) degrees C-1. (c) 2006 Elsevier Ltd. All rights reserved.