It was recalled that some forms of dense strain contrast in this material had been considered to be dislocation tangles that formed during mechanical milling. The present electron microscopic analyses indicated that strain contrast with radial contours could not be attributed to dislocations, but was instead due to sub-grain boundaries that were associated with nucleation of the crystal. It was concluded that a number of growth variants nucleated independently on the surface of a single Si-N cluster, coarsened and formed closure errors when they impinged; thus giving rise to the formation of sub-grain boundaries which extended from the core. The sub-grain boundaries were found to be located only on {100}, {110} and {101} planes of the β-Si3N4.

Structural Imperfection of β-Si3N4 Crystals Associated with Nucleation. F.F.Xu, Y.Bando, M.Zhang, C.M.Wang, M.Mitomo: Journal of Electron Microscopy, 2001, 50[3], 265-9