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Intermediate spin Fe 2+ in lower mantle perovskite

Intermediate spin Fe 2+ in lower mantle perovskite. C. McCammon, I. Kantor, O. Narygina, J. Rouquette, L. Dubrovinsky Bayerisches Geoinstitut, Universität Bayreuth, Germany U. Ponkratz, I. Sergueev, M. Mezouar ESRF, Grenoble, France V. Prakapenka APS, Chicago, USA. Second VLab Workshop

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Intermediate spin Fe 2+ in lower mantle perovskite

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  1. Intermediate spin Fe2+ in lower mantle perovskite C. McCammon, I. Kantor, O. Narygina, J. Rouquette, L. Dubrovinsky Bayerisches Geoinstitut, Universität Bayreuth, Germany U. Ponkratz, I. Sergueev, M. Mezouar ESRF, Grenoble, France V. Prakapenka APS, Chicago, USA Second VLab Workshop University of Minnesota August 5-10, 2007 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  2. Evidence for Fe2+ spin transition: XES Mg0.9Fe0.1SiO3 perovskite Badro et al. (2004) decrease of intensity means reduction of S C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  3. Evidence for Fe2+ spin transition: NFS Mg0.9Fe0.1SiO3 perovskite Fe2+ high spin Fe3+ high spin increase in QS with P McCammon (1998) Li et al. (2004) Jackson et al. (2005) C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  4. source DETECTOR DAC Mössbauer spectroscopy • Re gasket with 100 µm hole • 250 µm culet diamonds • starting material Fe0.12Mg0.88SiO3 and Mg0.86Fe0.14Si0.98Al0.02O3 • 61% enriched in 57Fe • synthesis in multianvil press and/or by laser heating (LH) in DAC • 16 different loadings of DAC • 119 spectra collected RT 0-89 GPa • mostly LH between measurements • collection time 1-2 days each C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  5. DAC nuclear forward scattering ESRF ID18 PRL system image plate Kirkpatrick-Baez multilayer mirror DAC C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  6. DAC nuclear forward scattering cont. • same DAC + sample as for Mössbauer experiments • beam size 4 µm x 20 µm • 4 bunch mode = 700 ns spacing between bunches • 15 spectra collected RT 7-110 GPa • collection time 1-2 hours each • high-resolution XRD collected for same DAC at numerous P C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  7. P evolution of Mössbauer spectra Fe0.12Mg0.88SiO3 high QS with narrow energy width C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  8. P evolution of NFS spectra Fe0.12Mg0.88SiO3 44 GPa 61 GPa 110 GPa high QS with narrow energy width C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  9. P evolution of hyperfine parameters Fe0.12Mg0.88SiO3 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  10. High-pressure XRD experiments → All reflections consistent with Pbnm perovskite at 110 GPa C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  11. Electronic structure of VIIIFe2+ C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  12. Other intermediate spin d6 compounds e.g., Co3+ in MCoO3 perovskites thermal expansion thermal conductivity LaCoO3 LaCoO3 IS→HS LS→IS Murata et al. 1999 Yan et al. 2004 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  13. Octahedral tilting in (Mg,Fe)SiO3 perovskite High-resolution XRD data collected at APS on IDD-13 Kudoh et al. 1987 Ross & Hazen 1990 Funamori et al. 1996 Mitchell 2002 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  14. Badro et al. 2004 Li et al. 2004 Spin number variation with pressure S = [(2 × Ahigh-spin Fe2+) + (1 × Aintermediate-spin Fe2+) + (5/2 × Ahigh-spin Fe3+)]/ΣA Fe0.12Mg0.88SiO3 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  15. Heated DAC Mössbauer spectroscopy C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  16. Heated DAC nuclear forward scattering C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  17. Pressure-temperature paths Fe0.12Mg0.88SiO3 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  18. Nuclear forward scattering 62 GPa 1000 K Fe2+ intermediate spin Spectra at high P,T Fe0.12Mg0.88SiO3 Mössbauer spectroscopy 55 GPa 800 K Fe2+ intermediate spin → Intermediate spin stable at higher T C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  19. Effect of Al3+ and Fe3+ on spin transition Mg0.86Fe0.14Si0.98Al0.02O3 • 5 sample loadings • 42 Mössbauer spectra • P = 0 to 70 GPa • T = 300 to 700 K → Fe2+ spin transition also occurs in the presence of trivalent cations C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  20. Spin number variation with P,T Fe0.12Mg0.88SiO3 Sturhahn et al. 2005 C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

  21. Summary • Fe2+ in (Mg,Fe)(Si,Al)O3 perovskite is predominantly intermediate spin throughout entire lower mantle • this conclusion is consistent with all existing data • spin transition in Fe3+ not required to explain data, but cannot be ruled out • spin transition might be coupled to lattice distortion. Variations in sample environment (e.g., deviatoric stress) can change spin state stability (already calculated by Li et al. 2005) • challenge to computational community to reproduce experimental results on spin state • return spotlight to perovskite phase to assess implications of spin state change for mantle properties and dynamics C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

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