@article{04b3b8ba54ab4373ba0bf419eac85b91,
title = "Electronic transitions of iron in almandine-composition glass to 91 GPa",
abstract = "Valence and spin states of Fe were investigated in a glass of almandine (Fe3Al2Si3O12) composition to 91 GPa by X-ray emission spectroscopy and energy-and time-domain synchrotron Mossbauer spectroscopy in the diamond-anvil cell. Changes in optical properties, total spin moment and Mossbauer parameters all occur predominantly between 1 bar and ~30 GPa. Over this pressure range, the glass changes from translucent brown to opaque and black. The total spin moment of the glass derived from X ray emission spectroscopy decreases by ~20%. The complementary Mossbauer spectroscopy approaches reveal consistent changes in sites corresponding to 80-90% Fe2+ and 10-20% Fe3+. The high-spin Fe2+ doublet exhibits a continuous decrease in isomer shift and increase in line width and asymmetry. A high-spin Fe3+ doublet with quadrupole splitting of ~1.2 mm/s is replaced by a doublet with quadrupole splitting of ~1.9 mm/s, a value higher than all previous measurements of high-spin Fe3+ and consistent with low-spin Fe3+. These observations suggest that Fe3+ in the glass undergoes a continual transition from a high-spin to a low-spin state between 1 bar and ~30 GPa. Almandine glass is not expected to undergo any abrupt transitions in electronic state at deep mantle pressures.",
keywords = "Mossbauer spectroscopy, Silicate glass, X ray emission spectroscopy, nuclear forward scattering, spin transitions",
author = "Dorfman, {Susannah M.} and Dutton, {Sian E.} and Vasily Potapkin and Chumakov, {Aleksandr I.} and Rueff, {Jean Pascal} and Paul Chow and Yuming Xiao and Cava, {Robert J.} and Duffy, {Thomas S.} and McCammon, {Catherine A.} and Philippe Gillet",
note = "Funding Information: We thank L. Dubrovinsky, I. Kupenko, S.-H. Shim, and C. Gu for helpful discussions about experiment design and interpretation. J. Wicks, G.J. Finkelstein, and C.V. Stan made suggestions that improved this manuscript. G. Poirier provided help with electron microscopy of starting materials. We acknowledge the usage of PRISM Imaging and Analysis Center that is supported in part by the NSF MRSEC program through the Princeton Center for Complex Materials (grant DMR-0819860). J. Delaney assisted with chemical analyses at the Rutgers University microprobe facility. E-SMS experiments were performed on the ID18 beamline at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. We are grateful to I. Kupenko at ERSF for providing assistance in using beamline ID18. J. Jacobs assisted with gas loading at the ESRF. T-SMS experiments were performed at the High Pressure Collaborative Access Team (HPCAT), Sector 16 of the Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOE-BES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Use of the COMPRES-GSECARS gas loading system was supported by COMPRES under NSF Cooperative Agreement EAR 11-57758 and by GSECARS through NSF grant EAR-1128799 and DOE grant DE-FG02-94ER14466. We acknowledge SOLEIL for provision of synchrotron radiation facilities for XES (Proposal ID 20130184) and we also thank B. Lassalle and J. Ablett for assistance in using beamline GALAXIES. Publisher Copyright: {\textcopyright} 2016 by Walter de Gruyter Berlin/Boston.",
year = "2016",
month = jul,
day = "1",
doi = "10.2138/am-2016-5606",
language = "English (US)",
volume = "101",
pages = "1659--1667",
journal = "American Mineralogist",
issn = "0003-004X",
publisher = "Mineralogical Society of America",
number = "7",
}