Effect of rare-earth oxide additives on the morphology of combustion synthesized rod-like $beta;-Si3N4 crystals

The results of synthesising rod-like beta-Si3N4 crystals by combustion synthesis with six rare-earth oxides (Y2O3, La2O3, CeO2, Sm2O3, Gd2O3 and Yb2O3) as additives under high nitrogen pressure are presented. The effect of rare-earth oxide additives on the final morphology of rod-like beta-Si3N4 was investigated and the crystal growth mechanism discussed. The results reveal that the final morphology of combustion synthesised Si3N4 is strongly dependent on the viscosity of liquid formed by the rare-earth oxide and the SiO2 on the Si powder surface. With increasing atomic number of the rare-earth elements, the final morphology changed from elongated rod-like crystals to short columnar crystals. 11 refs.