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6CCVD Research

Effects of composition and pressure on electronic states of iron in bridgmanite

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2020-02-06
JournalAmerican Mineralogist
AuthorsSusannah M. Dorfman, V. Potapkin, Mingda Lv, Eran Greenberg, Ilya Kupenko
InstitutionsSoreq Nuclear Research Center, Michigan State University
Citations11

Abstract

Section titled “Abstract”

Abstract 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. 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.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
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  3. 2004 - Electronic transitions in perovskite: Possible nonconvecting layers in the lower mantle [Crossref]
  4. 2015 - A compositional origin to ultralow-velocity zones
  5. 1993 - Mineralogical Applications of Crystal Field Theory
  6. 2010 - Spin and structural transitions in AlFeO3 and FeAlO3 perovskite and post-perovskite [Crossref]
  7. 2010 - Spin state of ferric iron in MgSiO3 perovskite and its effect on elastic properties [Crossref]
  8. 2011 - Effects of the Fe3+ spin transition on the properties of aluminous perovskite—New insights for lower-mantle seismic heterogeneities [Crossref]
  9. 2014 - Effect of Fe-enrichment on seismic properties of perovskite and post-perovskite in the deep lower mantle [Crossref]
  10. 2012 - Synthesis and equation of state of perovskites in the (Mg, Fe)3Al2Si3O12 system to 177 GPa [Crossref]

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