Synthesis of rod-like β-Si3N4 seed crystals with tailored morphology

β-Si3N4 seed crystals were synthesized by sintering (α+β)-Si3N4 powders with Y2O3+MgO additives at 1800 °C. Full α- to β-phase transformation was achievable at 1800 °C for 1 h. The pre-existing β-Si3N4 particles acted as nuclei during a sintering process. The length and mean aspect ratio of β-Si3N4 seed grains could be tailored by careful control of α/β-Si3N4 ratio, which resulted in various nuclei and driving force. The sample A95B5 with 5% β-nuclei shows a bimodal size distribution containing large amount of abnormal elongated β-Si3N4 grains with remarkable large diameter. With increasing the β-phase content from 5 wt% to 100 wt%, the average diameter and aspect ratio of the β-Si3N4 single crystals decreased from 1.43 µm to 0.92 µm and from 4.36 to 2.79, respectively.