High-resolution synchrotron X-ray powder diffraction and Rietveld structure refinement of two (Mg (sub 0.95) , Fe (sub 0.05) )SiO3perovskite samples synthesized under different oxygen fugacity conditions

Abstract

This paper presents high-resolution synchrotron X-ray powder diffraction data 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. Mössbauer smdies have indicated that Fe3/∑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 coordinated A site for both compositions. There appears to be no significant differences 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.