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Experimental and theoretical XANES and EXAFS study of tetra-ferriphlogopite

¹ Dip. di Scienze della Terra and INFM, Università di Camerino, I-62032 Camerino, Italy
² Beijing Synchrotron Radiation Facility, Institut of High Energy Physics, Chinese Academy of Sciences, PO box 918, 100039 Beijing, P.R. China
³ Dip. di Scienze della Terra, Università di Modena and Reggio Emilia, Largo S. Eufemia 19, I-41100 Modena, Italy
⁴ INFN-LNF, Via E. Fermi, I-00044 Frascati, Italy
⁵ Dip. di Scienze Geologiche, Università degli Studi di Roma Tre, Largo S. L. Murialdo 1, I-00146 Roma, Italy

^* E-mail:gabriele{at}camserv.unicam.it

Experimental and theoretical EXAFS and XANES data on Fe coordination and bond distances have been obtained for a natural tetra-ferriphlogopite. XANES data show a predominance of trivalent iron in tetrahedral coordination. The use of theoretical multiple scattering calculations helps distinguish the contributions to the total spectrum coming from the different iron atoms. EXAFS spectra were reduced and analyzed using the GNXAS programs and Fe has been confirmed to be in tetrahedral coordination, with refined structural data Fe-O = 1.86 Å, Fe-Si = 3.24 Å, Fe-O-Si = 138°. Moreover, a further contribution from Fe is detected corresponding to a Fe-O distance equal to 2.22 Å. This latter contribution (20 mol % of the total Fe ca.) is interpreted to arise from divalent Fe in octahedral coordination, in excellent agreement with the structural and chemical data.

Key-words: XAS, iron, micas, tetra-ferriphlogopite..

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