Pressure effect on the electronic structure of iron in (Mg,Fe)(Si,Al)O3 perovskite: a combined synchrotron Mössbauer and X-ray emission spectroscopy study up to 100 GPa

Abstract

We investigated the valence state and spin state of iron in an Al-bearing ferromagnesian silicate perovskite sample with the composition (Mg0.88Fe0.09) (Si0.94Al0.10)O3 between 1 bar and 100 GPa and at 300 K, using diamond cells and synchrotron Moss- bauer spectroscopy techniques. At pressures below 12 GPa, our Mossbauer spectra can be sufficiently fitted by a ''two-doublet'' model, which assumes one ferrous Fe 2+ -like site and one ferric Fe 3+ -like site with distinct hyperfine parameters. The simplest interpre- tation that is consistent with both the Mossbauer data and previous X-ray emission data on the same sample is that the Fe 2+ -like site is high-spin Fe 2+ , and the Fe 3+ -like site is high-spin Fe 3+ . At 12 GPa and higher pressures, a ''three-doublet'' model is necessary and sufficient to fit the Mossbauer spectra. This model assumes two Fe 2+ -like sites and one Fe 3+ -like site distinguished by their hyperfine parameters. Between