Control of β-Si3N4 crystal morphology and its mechanism (part 2) - Effect of lanthanide additives

Abstract

Alpha-Si3N4 powder mixed with SiO2 and Ln2O3 (Ln=La, Gd or Yb) was heat-treated at 1750-1900°C. After removing the glassy phase, the morphologies of β-Si3N4 crystals were quantitatively analyzed. The aspect ratios of β-Si3N4 crystals doped with different lanthanide oxides increased in the order of La2O3>Gd2O3> Yb2O3 at high annealing temperatures. The anisotropic Ostwald ripening model successfully simulated grain growth behaviors of β-Si3N4 with different lanthanide additives, and suggested that the observed difference in grain growth behaviors be due to the change in the reaction rate at the (100) interface between the β Si3N4 crystal and the Ln-Si-O-N liquid phase.