The α–β Transformation in Silicon Nitride Single Crystals

Abstract
Single crystals of α‐Si3N4 were annealed at 2000°–2150°C. The β phase was detected after annealing at 2150°C only when the crystals were surrounded by MgO·3Al2O3 or Y2O3 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 Si3N4.