Hj. Kleebe et al., STATISTICAL-ANALYSIS OF THE INTERGRANULAR FILM THICKNESS IN SILICON-NITRIDE CERAMICS, Journal of the American Ceramic Society, 76(8), 1993, pp. 1969-1977
Silicon nitride materials typically reveal thin amorphous intergranula
r films along grain boundaries, with only the exception of special bou
ndaries. It is known that such grain-boundary films strongly affect th
e high-temperature properties of the bulk material. High-resolution el
ectron microscopy (HREM) was used to study these amorphous films in di
fferent Si3N4 ceramics. The observed film thicknesses at grain boundar
ies in these materials varied between 5 and 15 angstrom. It was shown
that the grain-boundary film thickness strongly depends on film chemis
try. Careful inspections of film-thickness measurements across grain b
oundaries in a given material suggest that the film widths vary on the
order of 1 angstrom. Therefore, a quantitative evaluation should allo
w for the determination of the standard deviation of the film thicknes
s. The amorphous film widths along grain boundaries in four materials
were measured over the entire length (up to 1 mum) of the grain bounda
ry between two triple points. Forty to fifty data points were evaluate
d for each boundary, giving a Gaussian-like distribution of the film t
hickness around a median value, which corresponded well with the film
width measured from single HREM micrographs. The accuracy achieved by
the statistical method was better than +/- 1 angstrom.