Effect of Y2O3 on low temperature sintering and thermal conductivity of AlN ceramics

The effect Of Y2O3 on the densification and thermal conductivity of AlN ceramics sintered at the temperature of 1650 degreesC was studied using CaF2-Y2O3 system as additives. XRD was employed to identify the phases formed during sintering. The results show that AlN ceramics with Y2O3 addition have a low shrinkage at temperatures below 1600 degreesC because the solid reaction between Y2O3 and Al2O3 decreases the amount of the calcium aluminates liquid due to the consumption of Al2O3. At 1650 degreesC, Y2O3 promotes the densification due to the formation of liquid CaYAlO4. The observation by TEM and HREM reveals that the inhomogeneous grain-boundary phases containing different phase compositions move to the three-grain junctions to form discrete pockets during the sintering. The measurement of the lattice parameters and the thermal conductivity of AlN ceramics shows that Y2O3 has no prominent effect on the purification of the AlN lattice at this sintering temperature. The higher thermal conductivity in the presence Of Y2O3 mainly comes from the enhancement of the densification. (C) 2002 Elsevier Science Ltd. All rights reserved.