Intermediate spin Fe 2 in lower mantle perovskite

Intermediate spin Fe 2+ in lower mantle perovskite C. Mc. Cammon, 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. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Evidence for Fe 2+ spin transition: XES Mg 0. 9 Fe 0. 1 Si. O 3 perovskite decrease of intensity means reduction of S C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite Badro et al. (2004)

Evidence for Fe 2+ spin transition: NFS Mg 0. 9 Fe 0. 1 Si. O 3 perovskite Fe 2+ high spin Fe 3+ high spin Mc. Cammon (1998) Li et al. (2004) increase in QS with P Jackson et al. (2005) C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

source DAC Mössbauer spectroscopy • Re gasket with 100 µm hole • 250 µm culet diamonds • starting material Fe 0. 12 Mg 0. 88 Si. O 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 DETECTOR • collection time 1 -2 days each C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

DAC nuclear forward scattering ESRF ID 18 PRL system image plate Kirkpatrick-Baez multilayer mirror DAC C. Mc. Cammon: 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 7 -110 GPa • collection time 1 -2 hours each • high-resolution XRD collected for same DAC at numerous P C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

P evolution of Mössbauer spectra Fe 0. 12 Mg 0. 88 Si. O 3 high QS with narrow energy width C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

P evolution of NFS spectra Fe 0. 12 Mg 0. 88 Si. O 3 44 GPa 61 GPa 110 GPa high QS with narrow energy width C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

P evolution of hyperfine parameters Fe 0. 12 Mg 0. 88 Si. O 3 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

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

Electronic structure of VIIIFe 2+ C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Other intermediate spin d 6 compounds e. g. , Co 3+ in MCo. O 3 perovskites thermal expansion La. Co. O 3 IS→HS thermal conductivity La. Co. O 3 LS→IS Murata et al. 1999 Yan et al. 2004 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Octahedral tilting in (Mg, Fe)Si. O 3 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. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Spin number variation with pressure S = [(2 × Ahigh-spin Fe 2+) + (1 × Aintermediate-spin Fe 2+) + (5/2 × Ahigh-spin Fe 3+)]/ΣA Fe 0. 12 Mg 0. 88 Si. O 3 Badro et al. 2004 Li et al. 2004 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

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

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

Pressure-temperature paths Fe 0. 12 Mg 0. 88 Si. O 3 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Spectra at high P, T Fe 0. 12 Mg 0. 88 Si. O 3 Mössbauer spectroscopy 55 GPa 800 K Nuclear forward scattering 62 GPa 1000 K Fe 2+ intermediate spin → Intermediate spin stable at higher T C. Mc. Cammon: 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 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite

Spin number variation with P, T Fe 0. 12 Mg 0. 88 Si. O 3 Sturhahn et al. 2005 C. Mc. Cammon: 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 C. Mc. Cammon: Intermediate spin Fe 2+ in lower mantle perovskite