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Interpretation of Si‐L2,3 Edge Electron Energy Loss Near Edge Structures (ELNES) from Intergranular Glassy Film of Si3N4 Ceramics
Author(s) -
Yoshiya Masato,
Adachi Hirohiko,
Tanaka Isao
Publication year - 1999
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1999.tb02229.x
Subject(s) - intergranular corrosion , materials science , spectral line , tetrahedron , analytical chemistry (journal) , crystallography , atomic physics , condensed matter physics , chemistry , physics , microstructure , composite material , astronomy , chromatography
First‐principles molecular orbital calculations of model clusters for Si 3 N 4 , Si 2 N 2 O, SiO 2 crystals are made by the discrete variational (DV)‐Xalpha method in order to interpret features that appear in the Si‐ L 2,3 edge ELNES spectra. They are understood in terms of interaction among molecular orbitals for their structural units, i.e., [SiX 4 ] n‐ tetrahedra (X = N, O). Two parameters, i.e., the N/(N + O) ratio, M N , and the number of N atoms included in a unit tetrahedron, X N , are found to determine the spectral features. On the basis of this knowledge, spatially resolved ELNES from intergranular glassy films of high‐purity Si 3 N 4 ‐SiO 2 ceramics is interpreted. The shift in the first peak by 0.9 eV can be ascribed to M N = 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, [Si 7 N 13 O 7 ] 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.