We reveal the presence of atomic short-range ordering at the interface between crystalline ␤-Si 3 N 4 and amorphous SiO 2 using aberration-corrected scanning transmission electron microscopy. We show that the first atomic layers of the amorphous SiO 2 film reconstruct taking on the crystalline form of Si 3 N 4 . Furthermore, we find that there is a nonuniform interatomic mixing of oxygen and nitrogen at different atomic sites at the interface. The work provides a direct look at the atomic structure of crystal/amorphous interfaces composed of light elements.

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Strength, toughness, microstructure, and atomic adsorption arrangement in silicon nitrides with MgO and RE 2 O 3 additions (RE = La, Gd, Y, Lu) were examined. Mechanical properties were high for La, Gd, and equal La-Lu additions, but surprisingly were progressively lower for Y-and Lu-doped samples. The lower strength and toughness were associated with fewer visible crack deflections and grain bridges. Detailed microstructural analysis of the Lu-doped material revealed a complex intergranular nanostructure with variable Lu content and Si 3 N 4 nanocrystals. Furthermore, the Lu-rich areas showed an extra Lu-adsorption site on the Si 3 N 4 prismatic planes not previously observed in other studies. This inhomogeneous structure was attributed to grain growth impingement and higher viscosity of the Lu-doped oxynitride glass that slows homogenization. The Y-doped material with nearly identical glass viscosity demonstrates intermediate behavior. Finally, substituting half of the Lu 2 O 3 with La 2 O 3 resulted in a homogenous intergranular structure, attributed to a lower viscosity of the oxynitride glass phase, and high mechanical properties. Overall, care must be taken when adapting Si 3 N 4 processing parameters for the smaller ionic radius rare earth dopants such as Lu and Y.

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