GRAIN-BOUNDARY FILMS IN RARE-EARTH-GLASS-BASED SILICON-NITRIDE

The thickness of the intergranular films in Si3N4 densified with lanth anide oxides has been systematically investigated using high-resolutio n transmission electron microscopy. Four lanthanide oxides-La2O3, Nd2O 3, Gd2O3, and Yb2O3-as well as Y2O3 are chosen so that the results wil l reflect the overall trend in the effect of the lanthanide utilized. The film thicknesses increase with increasing ionic radius of the lant hanide. In addition, Si3N4 particles flocculated into isolated cluster s in the lanthanide-based glasses are also characteristically separate d by an amorphous film whose thickness is similar to that in the compa rable polycrystalline ceramics, demonstrating that the film thickness is dictated entirely by the composition and not by the amount of the g lass phase present.