Ab initio computation on the Fe L-edge X-ray emission spectroscopy of Fe-bearing MgSiO3 perovskite

Abstract

We systematically investigated the L -edge X-ray emission spectroscopy (XES), a 3 d -to-2 p transition, of Fe 2+ - and Fe 3+ -bearing MgSiO 3 perovskite under high pressure based on the internally consistent LSDA+ U technique combined with the Slater-transition method. The Fe L -edge XES spectra can be used to directly interpolate the distribution of Fe-3 d electrons including the spin states and coordination environments of iron. Our results show that the spin transition from the high-spin state to low-spin state of Fe 2+ and Fe 3+ can be identified easily by the L -edge XES technique. The valence state of Fe (2+ or 3+) can be verified by this, since a shift of the first main peak of Fe 2+ across the spin transition of 2 eV, in good agreement with the experimental value (~1.6 eV), is significantly smaller than that of Fe 3+ of 4 eV. The width of the L -edge XES of Fe 3+ also depends strongly on the substitution sites (Mg or Si), meaning that its coordination environments might also be distinguishable based on the Fe L -edge XES spectra. These strong sensitivities to the Fe’s states suggest that the high-resolution Fe L -edge XES would be a useful experimental technique to investigate Fe-bearing silicate minerals.