Pressure effect on the electronic structure of iron in Mg,Fe Si, Al O{sub 3} perovskite : a combined synchrotron Mossbauer and x-ray emission spectroscopy study up to 100 GPa.
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 M{umlt o}ssbauer spectroscopy techniques. At pressures below 12 GPa, our Mossbauer spectra can be sufficiently fitted by a ''two-doublet'' model, which assumes one ferrous Fe2+-like site and one ferric Fe3+-like site with distinct hyperfine parameters. The simplest interpretation that is consistent with both the M{umlt o}ssbauer data and previous X-ray emission data on the same sample is that the Fe2+-like site is high-spin Fe2+, and the Fe3+-like site is high-spin Fe3+. At 12 GPa and higher pressures, a ''three-doublet'' model is necessary and sufficient to fit the Mossbauer spectra. This model assumes two Fe2+-like sites and one Fe3+-like site distinguished by their hyperfine parameters. Between 12 and 20 GPa, the fraction of the Fe3+-like site, Fe3+/{Sigma}Fe, changes abruptly from about 50 to 70%, possibly due to a spin crossover in six-coordinate Fe2+. At pressures above 20 GPa, the fractions of all three sites remain unchanged to the highest pressure, indicating a fixed valence state of iron within this pressure range. From 20 to 100 GPa, the isomer shift between the Fe3+-like and Fe2+-like sites increases slightly, while the values and widths of the quadruple splitting of all three sites remain essentially constant. In conjunction with the previous X-ray emission data, the Mossbauer data suggest that Fe2+ alone, or concurrently with Fe3+, undergoes pressure-induced spin crossover between 20 and 100 GPa.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); Lawrence Livermore Fellowship
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 914926
- Report Number(s):
- ANL/XSD/JA-58408; TRN: US0804848
- Journal Information:
- Phys. Chem. Miner., Vol. 33, Issue 8-9 ; Nov. 2006
- Country of Publication:
- United States
- Language:
- ENGLISH
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