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C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Intermediate spin Fe 2+ in lower mantle perovskite C. McCammon, I. Kantor, O. Narygina,

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Presentation on theme: "C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Intermediate spin Fe 2+ in lower mantle perovskite C. McCammon, I. Kantor, O. Narygina,"— Presentation transcript:

1 C. McCammon: 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 University of Minnesota August 5-10, 2007

2 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Evidence for Fe 2+ spin transition: XES Badro et al. (2004) Mg 0.9 Fe 0.1 SiO 3 perovskite decrease of intensity means reduction of S

3 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Evidence for Fe 2+ spin transition: NFS Li et al. (2004) Mg 0.9 Fe 0.1 SiO 3 perovskite Fe 2+ high spin Fe 3+ high spin McCammon (1998) increase in QS with P Jackson et al. (2005)

4 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite DAC Mössbauer spectroscopy DETECTOR source Re gasket with 100 µm hole 250 µm culet diamonds starting material Fe 0.12 Mg 0.88 SiO 3 and Mg 0.86 Fe 0.14 Si 0.98 Al 0.02 O 3 61% enriched in 57 Fe 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

5 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite DAC nuclear forward scattering ESRF ID18 Kirkpatrick-Baez multilayer mirror PRL system image plate DAC

6 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite 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 GPa collection time 1-2 hours each high-resolution XRD collected for same DAC at numerous P

7 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite P evolution of Mössbauer spectra high QS with narrow energy width Fe 0.12 Mg 0.88 SiO 3

8 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite P evolution of NFS spectra 44 GPa 61 GPa 110 GPa high QS with narrow energy width Fe 0.12 Mg 0.88 SiO 3

9 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite P evolution of hyperfine parameters Fe 0.12 Mg 0.88 SiO 3

10 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite High-pressure XRD experiments → All reflections consistent with Pbnm perovskite at 110 GPa

11 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Electronic structure of VIII Fe 2+

12 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Other intermediate spin d 6 compounds e.g., Co 3+ in MCoO 3 perovskites Yan et al. 2004Murata et al LaCoO 3 LS→IS IS→HS thermal expansionthermal conductivity

13 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Octahedral tilting in (Mg,Fe)SiO 3 perovskite High-resolution XRD data collected at APS on IDD-13 Kudoh et al Ross & Hazen 1990 Funamori et al Mitchell 2002

14 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Spin number variation with pressure S = [(2 × A high-spin Fe2+ ) + (1 × A intermediate-spin Fe2+ ) + (5/2 × A high-spin Fe3+ )]/ΣA Badro et al Li et al Fe 0.12 Mg 0.88 SiO 3

15 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Heated DAC Mössbauer spectroscopy

16 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Heated DAC nuclear forward scattering

17 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Pressure-temperature paths Fe 0.12 Mg 0.88 SiO 3

18 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Spectra at high P,T 55 GPa 800 K Mössbauer spectroscopy Fe 2+ intermediate spin 62 GPa 1000 K Nuclear forward scattering Fe 2+ intermediate spin → Intermediate spin stable at higher T Fe 0.12 Mg 0.88 SiO 3

19 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Effect of Al 3+ and Fe 3+ on spin transition Mg 0.86 Fe 0.14 Si 0.98 Al 0.02 O 3 5 sample loadings 42 Mössbauer spectra P = 0 to 70 GPa T = 300 to 700 K → Fe 2+ spin transition also occurs in the presence of trivalent cations

20 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Spin number variation with P,T Sturhahn et al Fe 0.12 Mg 0.88 SiO 3

21 C. McCammon: Intermediate spin Fe 2+ in lower mantle perovskite Summary Fe 2+ in (Mg,Fe)(Si,Al)O 3 perovskite is predominantly intermediate spin throughout entire lower mantle this conclusion is consistent with all existing data spin transition in Fe 3+ 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


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