The α-β Transformation in Silicon Nitride Single Crystals

Single crystals of alpha-Si3N4 were annealed at 2000 degrees-2150 degrees C. The beta phase was detected after annealing at 2150 degrees C only when the crystals were surrounded by MgO . 3Al(2)O(3) or Y2O3 powders. On the other hand, no evidence of the alpha-beta transformation was found when the crystals were annealed without additives. The solution-precipitation mechanism was concluded to be the dominant factor in the alpha-beta transformation of Si3N4.