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

This paper presents the results of synthesizing rod-like beta-Si3N4 crystals by combustion synthesis (CS) with six rare-earth oxides (Y2O3, La2O3, CeO2, Sm2O3, Gd2O3 and Yb2O3) as additives under high nitrogen pressure. The effect of rare-earth oxide additives on the final morphology of rod-like beta-Si3N4 was investigated and the crystal growth mechanism was discussed in detail. The results reveal that the final morphology of combustion synthesized Si3N4 is strongly dependent on the viscosity of liquid formed by the rare-earth oxide and the SiO2 on the Si powder surface. With the increasing of atomic number of the rare-earth elements, the final morphology is from elongated rod-like crystals to short columnar crystals. (C) 2004 Elsevier B.V. All rights reserved.