Interpretation of Si-L2,3 Edge Electron Energy Loss Near Edge Structures (ELNES) from Intergranular Glassy Film of Si3N4 Ceramics

First‐principles molecular orbital calculations of model clusters for Si3N4, Si2N2O, SiO2 crystals are made by the discrete variational (DV)‐Xalpha method in order to interpret features that appear in the Si‐L2,3 edge ELNES spectra. They are understood in terms of interaction among molecular orbitals for their structural units, i.e., [SiX4]n‐ tetrahedra (X = N, O). Two parameters, i.e., the N/(N + O) ratio, MN, and the number of N atoms included in a unit tetrahedron, XN, are found to determine the spectral features. On the basis of this knowledge, spatially resolved ELNES from intergranular glassy films of high‐purity Si3N4‐SiO2 ceramics is interpreted. The shift in the first peak by 0.9 eV can be ascribed to MN= 0.43 ± 0.06 in the intergranular film. The N content satisfactorily agrees with that determined by line‐profiling of ELNES. Broadening of the first peak can also be explained consistently by considering this amount of N in the glassy film. An example model‐cluster of the glassy film, [Si7N13O7]25‐ is found sufficient to reproduce the ELNES from the glassy film without inclusion of further complexity or inhomogeneity. The presence of N in the intergranular film is proposed to be the result of the topological requirement imposed by the absence of a broken bond. A model structure that may be useful for further structural optimization is given.