Sintering behavior and thermal conductivity of AIN ceramics with Y2O3-Al2O3 additives having eutectic composition

We investigated sintering behavior and thermal conductivity of AlN ceramics sintered with sintering additives having the eutectic point composition (at 1760degreesC) in the phase diagram of the Y2O3-Al2O3 system. We used two kinds of additives, which were 2 mass%: Y2O3-3 mass%: Al2O3, and 4 mass%: Y2O3-6 mass%: Al2O3. In the sintering temperature range of 1600-1700degreesC, the shrinkage of the samples increased, and the formation of neck between the AlN particles progressed with the increasing temperature, while the lattice parameter c of the crystal lattice in the AlN particle contracted. It was suggested that the particle growth due to the neck formation related with the contraction of the c parameter although the size and shape of the AlN particle were still small and round in the temperature range. However, for the samples sintered at 1750degreesC, the size and shape unexpectedly increased and became hexagonal. The sudden changes of the size and shape nearly depended on the sintering temperature almost independent of sintering time (0.5-5 h). The results seem to suggest an important relation between full densification of AlN and liquefaction of the sintering additives. Thermal conductivity I of the samples was very low value, which seems to depend on high oxygen concentration n in the AlN lattice. Further, the relation between thermal resistance (1/lambda) and the oxygen concentration (n) did not strictly depend on the Slack's law for the relation for fully densified AlN ceramics. There seemed to be other factors on the low thermal conductivity.