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X‐ray Absorption Near‐Edge Structure of Grain‐Boundary‐Segregated Y and Zr in Creep‐Resistant Alumina
Author(s) -
Wang C. M.,
Cargill G. Slade,
Chan Helen M.,
Harmer Martin P.
Publication year - 2002
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.1151-2916.2002.tb00486.x
Subject(s) - xanes , grain boundary , materials science , crystallography , extended x ray absorption fine structure , absorption (acoustics) , analytical chemistry (journal) , chemistry , metallurgy , absorption spectroscopy , spectral line , microstructure , composite material , physics , optics , chromatography , astronomy
X‐ray absorption near‐edge structure (XANES) depends on stereochemical features of coordination polyhedra around probe atoms. K ‐edge XANES of Y and Zr segregated in alumina grain boundaries has been obtained and analyzed using metallic Y and Zr, Y 2 O 3 , YAG, and monoclinic ZrO 2 as standards. Grain‐boundary‐segregated Y and Zr show a positive chemical shift, and the magnitude of the shift, as compared with that of Y 2 O 3 and ZrO 2 , respectively, is different for Y and Zr, indicating that, relative to Y 2 O 3 and ZrO 2 , charge transfers for the grain‐boundary‐segregated Y and Zr are different. This result is also supported by the strength of the threshold resonance. A pre‐edge shoulder is seen in K ‐edge XANES for grain‐boundary‐segregated Y and Zr but not for Y 2 O 3 and ZrO 2 . This shoulder is attributed to the 1 s → 4 d transition, which is normally forbidden, but can occur because of d – p mixing, which is favored by a tetrahedral coordination configuration. These results suggest that some of the grain‐boundary‐segregated Y and Zr have coordination configurations with a well‐defined tetrahedral symmetry. The XANES results are compared with those obtained from EXAFS. Implications of these results for understanding of the enhanced creep resistance in alumina are also discussed.