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

The electronic spin and valence states of Fe in post‐perovskite ((Mg0.75Fe0.25)SiO3) have been investigated by synchrotron X‐ray diffraction, Mössbauer 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 Mössbauer 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 CaIrO3‐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.