Grain‐Boundary Microstructure and Chemistry of a Hot Isostatically Pressed High‐Purity Silicon Nitride

Abstract

Two high‐purity Si 3 N 4 materials were fabricated by hot isostatic pressing without the presence of sintering additives, using an amorphous laser‐derived Si 3 N 4 powder with different oxygen contents. High‐resolution transmission electron microscopy and electron energy‐loss spectroscopy (EELS) analysis of the Si 3 N 4 materials showed the presence of an amorphous SiO 2 grain‐boundary phase in the three‐grain junctions. Spatially resolved EELS analysis indicated the presence of a chemistry similar to silicon oxynitride at the two‐grain junctions, which may be due to partial dissolution of nitrogen in the grain‐boundary film. The chemical composition of the grain‐boundary film was SiN x O y , (x ∼ 0.53 and y ∼ 1.23), and the triple pocket corresponded to the amorphous SiO 2 containing ∼2 wt% nitrogen. The equilibrium grain‐boundary‐film thickness was measured and found to be smaller for the material with the lower oxygen content. This difference in thickness has been explained by the presence of the relatively larger calcium concentration in the material with the lower amount of SiO 2 grain‐boundary phase, because the concentration of foreign ions has been shown to affect the grain‐boundary thickness.