Jump to ContentJump to Main Navigation
Show Summary Details
More options …

American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2017: 2.645

CiteScore 2017: 2.31

SCImago Journal Rank (SJR) 2017: 1.440
Source Normalized Impact per Paper (SNIP) 2017: 1.059

Online
ISSN
1945-3027
See all formats and pricing
More options …
Volume 100, Issue 8-9

Issues

Recoil-free fractions of iron in aluminous bridgmanite from temperature-dependent Mössbauer spectra

Jiachao Liu
  • Corresponding author
  • Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, U.S.A.
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Bjorn Mysen / Yingwei Fei / Jie Li
  • Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, Michigan 48109, U.S.A.
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2015-08-12 | DOI: https://doi.org/10.2138/am-2015-5245

Abstract

Aluminous bridgmanite (Al-Bm) is the dominant phase in the Earth’s lower mantle. In this study, the Mössbauer spectra of an Al-Bm sample Mg0.868Fe0.087Si0.944Al0.101O2.994 were recorded from 65 to 300 K at 1 bar. The temperature dependence of the center shift was fitted by the Debye model and yielded the Debye temperatures of 305 ± 3 K for Fe2+ and 361 ± 22 K for Fe3+. These values are lower than those of Al-free bridgmanite by 17 and 24%, respectively, indicating that the presence of Fe and Al increases the average Fe-O bond length and weakens the bond strength. At 300 K, the calculated recoil-free fractions of Fe2+ (0.637 ± 0.006) and Fe3+ (0.72 ± 0.02) are similar and therefore the molar fractions of Fe2+ and Fe3+ are nearly the same as the area fractions of the corresponding Mössbauer doublets. At 900 K, the calculated recoil-free fractions of Fe3+ is 46% higher than that of Fe2+, implying that the molar fraction of Fe3+ is only 41% for a measured spectral area fraction of 50%, and that the area fractions of iron sites may change with temperature without any changes in the valence state or spin state of iron. We infer that Fe3+ accounts for 46 ± 2% of the iron in the Al-Bm and it enters the A site along with Al3+ in the B site through the coupled-substitution mechanism. An Fe2+ component with large quadrupole splitting (~4.0 mm/s) was observed at cryogenic conditions and interpreted as a high-spin distorted iron site.

Keywords: Mössbauer spectroscopy; aluminous bridgmanite; ferric iron; recoil-free fraction; Debye temperature; crystallographic site; lower mantle

About the article

Received: 2014-11-07

Accepted: 2015-02-23

Published Online: 2015-08-12

Published in Print: 2015-08-01


Citation Information: American Mineralogist, Volume 100, Issue 8-9, Pages 1978–1984, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-5245.

Export Citation

© 2015 by Walter de Gruyter Berlin/Boston.

Comments (0)

Please log in or register to comment.
Log in