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

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 (Mg_0.95Fe_0.05)SiO₃ synthesized at 25 GPa and 1920 K in a multi-anvil press at different oxygen fugacity conditions. Mossbauer studies have indicated that Fe³⁺/ΣFe 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.