THE SITE OF FE IN FE-BEARING MGSIO3 ENSTATITE AND PEROVSKITE - A THEORETICAL, X-RAY MULTIPLE-SCATTERING STUDY AT FE K-EDGE

Two polycrystalline-, Fe-bearing MgSiO3 enstatite and perovskite have been probed by x-ray absorption near edge structure (XANES) spectrosco py at the Fe K-edge under ambient conditions. The perovskite sample wa s synthesized at 260 kbar and 1973 K in a multianvil apparatus. The ex perimental XANES spectrum has been compared to ab-initio-, x-ray multi ple-scattering calculations (Feff 6 code). Calculations confirm that t he Fe K-edge arises mainly from multiple scattering involving the firs t shell of oxygen neighbors around Fe. In Fe-enstatite, these calculat ions are consistent with Fe2+ as substituted in the M2 site of this or thopyroxene, in good agreement with crystal structure refinements and previous XANES studies. In perovskite, Feff 6 suggests that Fe is like ly to be substituted to Mg within the (8 + 4)-coordinated sites of tha t perovskite. No evidences for 6-coordinated Fe were found. These resu lts are consistent with a previous anharmonic analysis of the extended x-ray absorption fine structure (EXAFS) study that evidenced the pres ence of 8-coordinated Fe in the same perovskite sample.