The α–β Transformation in Silicon Nitride Single Crystals

Single crystals of α‐Si 3 N 4 were annealed at 2000°–2150°C. The β phase was detected after annealing at 2150°C only when the crystals were surrounded by MgO·3Al 2 O 3 or Y 2 O 3 powders. On the other hand, no evidence of the α–β transformation was found when the crystals were annealed without additives. The solution–precipitation mechanism was concluded to be the dominant factor in the α–β transformation of Si 3 N 4 .