The Influence of ZrO ₂ Additions on Al ₂ O ₃ Evaporation and AlN Crystal Growth by Thermal Nitridation of Al ₂ O ₃ – ZrO ₂ Pellets

Abstract

The effects of ZrO 2 additions to Al 2 O 3 were investigated to improve the evaporation rate of Al 2 O 3 for bulk AlN crystal growth. The evaporation rate of Al 2 O 3 increased concomitantly with increasing ZrO 2 concentration under a nitrogen gas stream at 2223 K. The ZrO 2 was predominantly nitrided. The nitridation of ZrO 2 kept the local oxygen partial pressure high at the pellet surface, which suppressed the nitridation of Al 2 O 3 . The nitridation of ZrO 2 caused the outward diffusion of ZrO 2 (Zr 4+ and O 2− ) in the pellet, which was accelerated further by the presence of Al 2 O 3 –ZrO 2 liquid phase in grain boundaries, leading to the prompt formation of ZrN porous layer on the pellet surface. The suppressed nitridation of Al 2 O 3 and the formation of porous ZrN layer were the reasons for the enhanced evaporation of Al 2 O 3 , leading to enhanced bulk AlN growth.