Národní geovědní bibliografie - GeoLib: Podrobnosti záznamu

High-resolution Fe K-edge XANES spectra of a series of crystalline Fe2+ and Fe3+ -bearing model compounds were measured in an effort to correlate characteristics of the pre-edge feature with oxidation state and local coordination environment of Fe atoms. The model compounds comprise 30 natural minerals and synthetic compounds, with Fe coordination environments ranging from 4 to 12 O atoms for Fe2+, including 5-coordinated trigonal bipyramidal Fe2+, and from 4 to 6 O atoms for Fe3+. Most pre-edge spectra show two components (due to crystal field splitting) that are located just above the Fermi level. The most useful characteristics of the Fe-K pre-edge for determining Fe oxidation state and coordination number are the position of its centroid and its integrated intensity. The separation between the average pre-edge centroid positions for Fe2+ and Fe3+ is 1.4˝0.1 eV.

Thus, the position of the pre-edge feature can be used as a measure of the average Fe-redox state, with the average pre-edge position for mixed Fe2+-Fe3+ compounds occurring between positions for Fe2+ and Fe3+. The lowest pre-edge normalized heights and intergrated intensities are observed for the most centrosymmetric sites of Fe, in agreement with previous studies (see Waychunas et al. 1983). Examination of the pre-edge features of mechanical mixtures of phases containing different proportions of Fe2+ and Fe3+ suggests that the pre-edge position and intensity for these mixtures can vary quite non-linearly with the average redox state of Fe

Přispěvatel

Česká geologická služba

Kód přispěvatele

ČGS (UNM)

Zdrojový formát

Datum vložení

21. 8. 2007

Datum importu

8. 8. 2012