Statistical Analysis of the Intergranular Film Thickness in Silicon Nitride Ceramics

TLDR

Silicon nitride ceramics contain thin amorphous intergranular films that influence high‑temperature properties, with widths typically varying by about 1 Å. The study aimed to quantify the standard deviation of film thickness across grain boundaries. High‑resolution electron microscopy was employed to measure film widths along entire grain boundaries up to 1 µm in four Si₃N₄ materials. Film thicknesses ranged from 5 to 15 Å, varied with chemistry, followed a Gaussian‑like distribution with a median matching HREM measurements, and were determined with an accuracy better than ±1 Å.

Abstract

Silicon nitride materials typically reveal thin amorphous intergranular films along grain boundaries, with only the exception of special boundaries. It is known that such grainboundary films strongly affect the high‐temperature properties of the bulk material. High‐resolution electron microscopy (HREM) was used to study these amorphous films in different Si 3 N 4 ceramics. The observed film thicknesses at grain boundaries in these materials varied between 5and 15 Å. It was shown that the grain‐boundary film thickness strongly depends on film chemistry. Careful inspections of film‐thickness measurements across grain boundaries in a given material suggest that the film widths vary on the order of 1 Å. Therefore, a quantitative evaluation should allow for the determination of the standard deviation of the film thickness. The amorphous film widths along grain boundaries in four materials were measured over the entire length (up to 1 μm) of the grain boundary between two triple points. Forty to fifty data points were evaluated for each boundary, giving a Gaussian‐like distribution of the film thickness 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 Å.