IRON SITE GEOMETRY IN ORTHO-PYROXENE - MULTIPLE-SCATTERING CALCULATIONS AND XANES STUDY

The iron site geometry in orthopyroxenes (OPX) and synthetic FeO, has been investigated by X-ray Absorption Near Edge Structure (XANES) spec troscopy. Multiple scattering calculations have been used to determine how the iron polyhedral geometry affects the absorption spectra. The results reported here demonstrate that this approach is effective in d etermining the site geometry around the absorbing atom, allowing the a ssignment of features in the XANES spectrum to specific structural asp ects of the coordination environment. In the case of the orthopyroxene s this method allows discrimination between the multiple scattering co ntributions to the absorption spectrum due to the two octahedral sites M 1 and M 2 of the OPX structure. The results obtained with the MS ca lculation were used to evaluate the effects of polyhedral distortion, symmetry changes and iron site occupancies on the experimental spectra . The results indicate a more quantitative way to interpret XANES expe rimental spectra and give insights into the interpretation of site geo metries of more complex or unknown structures and amorphous materials.