High-resolution synchrotron X-ray powder diffraction and Rietveld structure refinement of two (Mg0.95Fe0.05)SiO3 perovskite samples synthesized underdifferent oxygen fugacity conditions

This paper presents high-resolution synchrotron X-ray powder diffraction da ta at 290 K on two Fe-bearing, polycrystalline silicate perovskite samples with approximate compositions (Mg0.95Fe0.05)SiO3 synthesized at 25 GPa and 1920 K in a multi-anvil press at different oxygen fugacity conditions. Moss bauer studies have indicated that Fe3+/Sigma Fe for the samples are 0.09 +/ - 0.01 and near 0.16 +/- 0.03. Rietveld structural refinements confirm that Fe2+ and Fe3+ dominantly substitute for Mg2+ in the 8-fold to 12-fold coor dinated A site for both compositions. There appears to be no significant di fferences in the bond distances for these amounts of Fe3+ and no conclusive structural evidence to support indications from Mossbauer experiments that Fe3+ may occupy both A and B sites. To explore the effect of valence state further, this study also reports the first diffraction patterns of (Mg,Fe) SiO3 perovskite collected at a wavelength near the Fe absorption edge.