Electronic spin and valence states of Fe in CaIrO3-type silicate post-perovskite in the Earth's lowermost mantle

Abstract

The electronic spin and valence states of Fe in post-perovskite ((Mg 0.75Fe0.25)SiO3) have been investigated by synchrotron X-ray diffraction, Mssbauer and X-ray emission spectroscopy at 142 GPa and 300 K. Rietveld refinement of the X-ray diffraction patterns revealed that our sample was dominated by CaIrO3-type post-perovskite. Combined Mssbauer and X-ray emission results show that Fe in post-perovskite is predominantly Fe2+ (70%) in the intermediate-spin state with extremely high quadrupole splitting of 3.77(25) mm/s. The remaining 30% Fe can be assigned to two sites. Compared with recent studies, our results indicate that the intermediate-spin Fe2+ is stabilized in CaIrO 3-type post-perovskite over a wide range of Fe content, whereas the low-spin Fe3+ is more dominant in the 2 × 1 kinked post-perovskite structure. The characterization of these structural and compositional effects on the spin and valence states of Fe in post-perovskite can help in understanding the geochemical and geophysical behavior of the core-mantle region. © 2010 by the American Geophysical Union.