Effects of composition and pressure on electronic states of iron in bridgmanite
[12];
- Michigan State Univ., East Lansing, MI (United States); Ecole Polytechnique Federale Lausanne (Switzlerland). Earth and Planetary Science Lab.
- University of Münster (Germany)
- Michigan State Univ., East Lansing, MI (United States)
- Tel-Aviv Univ. (Israel); Soreq Nuclear Research Center (NRC), Yavne (Israel)
- University of Münster (Germany); European Synchrotron Radiation Facility (ESRF), Grenoble (France)
- European Synchrotron Radiation Facility (ESRF), Grenoble (France)
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS); Univ. of Illinois at Urbana-Champaign, IL (United States); Univ. of Alabama, Birmingham, AL (United States)
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Ecole Polytechnique Federale Lausanne (Switzlerland). Crystal Growth Facility
- Princeton Univ., NJ (United States); Univ. of Cambridge (United Kingdom). Cavendish Lab.
- Princeton Univ., NJ (United States)
- Univ. of Bayreuth (Germany)
- Ecole Polytechnique Federale Lausanne (Switzlerland). Earth and Planetary Science Lab.
Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mössbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mössbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10–50% Fe/total cations, 0–25% Al/total cations, 12–100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mössbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at ~70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mössbauer sites with center shift ~1 mm/s and quadrupole splitting 2.4–3.1 and 3.9 mm/s at ~70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. Furthermore, in Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to ~20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- Sponsoring Organization:
- National Science Foundation (NSF); Swiss National Science Foundation (SNSF); USDOE Office of Science (SC), Office of Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC02-06CH11357
- OSTI ID:
- 1756034
- Journal Information:
- American Mineralogist, Vol. 105, Issue 7; ISSN 0003-004X
- Publisher:
- Mineralogical Society of AmericaCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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