Mitsuo Kasori

Thermal conductivity improvement of YAG added A1N ceramics in the grain boundary elimination process

Abstract The primary cause of the thermal conductivity improvement in Y 2 O 3 -containing AlN ceramics caused by elimination of the grain boundary phase was investigated. Y 3 Al 5 O 12 (YAG)-containing AlN powder compacts were sufficiently densified by firing at 1800 °C for 30 min, but had low thermal conductivity (90–110 Wm −1 K −1 ). Improvement to 245 Wm −1 K −1 and elimination of the grain boundary phases was brought about by annealing in a carbo-reductive atmosphere at 1850 °C for up to 100 h. During annealing, YAlO 3 , Y 4 Al 2 O 9 and Y 2 O 3 appeared as a result of the reduction-nitridation of the Al 2 O 3 constituent in the YAG. Subsequently, these yttrium rich phases acted as oxygen getters for the dissolved Al 2 O 3 which was originally included in the AlN grains. The Al 2 O 3 continuously changed into AlN by reduction-nitridation. The cyclic oxygen removal from the AlN through the grain boundary phase composition change is seen as the primary cause for the thermal conductivity improvement.