Spin transition and substitution of Fe3+ in Al-bearing post-Mg-perovskite

Abstract

The spin transition and substitution of Fe3+ in Mg0.85Fe3+0.15Al0.15Si0.85O3 post-Mg-perovskite (PPv) synthesized at 165–170GPa, 2100K were examined by X-ray emission spectroscopy (XES) and X-ray diffraction (XRD) during decompression to 37GPa without annealing. XRD showed that samples were single phase PPv down to 49GPa, although the samples may have partly become amorphous. The result of XES measurement indicates that Fe3+ is fully low spin (LS) for 165–100GPa and Fe3+ largely changes from LS to high spin (HS) between 80 and ∼40GPa. These results combined with previous reports indicate that Al and LS Fe3+ may occupy the A-(dodecahedral) and B-(octahedral) sites, respectively, as the favorable cation sites for 165–100GPa in Al-bearing PPv. Based on the present results on Fe3+ and recent theoretical reports on Fe2+, the spin states of iron in lower mantle PPv are discussed.