ISSN:
1600-5767
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Geosciences
,
Physics
Notes:
X-ray absorption fine spectra at the Al K edge were measured experimentally and calculated theoretically via the multiple-scattering formalism for chemically pure and physically perfect synthetic α-Al2O3 (α-alumina), natural ruby/sapphire (corundum) and a series of artificial corundums produced for technical purposes and used as geochemical standards. The Al K-edge spectra differ, despite the identical coordination (short-range arrangement) assumed by O around Al, and vary slightly in relation to the slightly different chemistries of the materials (substitutional defects) as well as on account of the location taken by foreign atoms in the structural lattices (positional defects). A quantitative treatment of the observed changes is made in terms of short-range distortion of the coordination polyhedron and of medium- to long-range modifications in the overall structure, both induced by substitutions. In some technical corundums, the impurities of admixed β-alumina, where Al is both in fourfold and sixfold coordination, produce another small but detectable effect on Al K edges. Therefore, XAFS spectroscopy proves its potential for both measuring a light element such as Al and detecting minor coordination changes and dilute substitutions (∼1–3 wt% as oxide) of the absorber by other atoms, at least under the favourable conditions occurring in this system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0021889898007778
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