Grain boundary films in rare-earth-glass-based silicon nitride

The thickness of the intergranular films in Si3N4 densified with
lanthanide oxides has been systematically investigated using
high-resolution transmission electron microscopy. Four lanthanide
oxides-La2O3, Nd2O3, Gd2O3, and Yb2O3-as well as Y2O3 are chosen so
that the results will reflect the overall trend in the effect of the
lanthanide utilized. The film thicknesses increase with increasing
ionic radius of the lanthanide. In addition, Si3N4 particles
flocculated into isolated clusters in the lanthanide-based glasses are
also characteristically separated by an amorphous film whose thickness
is similar to that in the comparable polycrystalline ceramics,
demonstrating that the film thickness is dictated entirely by the
composition and not by the amount of the glass phase present.