C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Intermediate spin FeIntermediate spin Fe2+2+ in lower mantle perovskite in lower mantle perovskite

C. McCammon, I. Kantor, O. Narygina, J. Rouquette, L. DubrovinskyBayerisches Geoinstitut, Universität Bayreuth, Germany

U. Ponkratz, I. Sergueev, M. MezouarESRF, Grenoble, France

V. PrakapenkaAPS, Chicago, USA

Second VLab WorkshopUniversity of Minnesota

August 5-10, 2007

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Evidence for FeEvidence for Fe2+2+ spin transition: XES spin transition: XESBadro et al. (2004)Mg0.9Fe0.1SiO3 perovskite

decrease of intensitymeans

reduction of S

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Evidence for FeEvidence for Fe2+2+ spin transition: NFS spin transition: NFS

Li et al. (2004)

Mg0.9Fe0.1SiO3 perovskite

Fe2+ high spin

Fe3+ high spin

McCammon (1998) increase in QS with P

Jackson et al. (2005)

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

DAC Mössbauer spectroscopyDAC Mössbauer spectroscopy

DETECTOR

so

urc

e

• 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

DAC nuclear forward scatteringDAC nuclear forward scatteringESRF ID18

Kirkpatrick-Baez multilayer mirrorKirkpatrick-Baez multilayer mirror

PRL systemPRL system

image plateimage plate

DACDAC

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

DAC nuclear forward scattering DAC nuclear forward scattering cont.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

P evolution of Mössbauer spectraP evolution of Mössbauer spectra

high QS withnarrow energy

width

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

P evolution of NFS spectraP evolution of NFS spectra

44 GPa

61 GPa

110 GPa high QS withnarrow energy

width

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

P evolution of hyperfine parametersP evolution of hyperfine parametersFe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

High-pressure XRD experiments High-pressure XRD experiments

→ All reflections consistent with Pbnm perovskite at 110 GPa

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Electronic structure of Electronic structure of VIIIVIIIFeFe2+2+

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Other intermediate spin Other intermediate spin dd66 compounds compoundse.g., Co3+ in MCoO3 perovskites

Yan et al. 2004Murata et al. 1999

LaCoO3 LaCoO3

LS→IS

IS→HS

thermal expansion thermal conductivity

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Octahedral tilting in (Mg,Fe)SiOOctahedral tilting in (Mg,Fe)SiO33 perovskite perovskiteHigh-resolution XRD data collected at APS on IDD-13

Kudoh et al. 1987Ross & Hazen 1990Funamori et al. 1996

Mitchell 2002

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Spin number variation with pressureSpin number variation with pressure

S = [(2 × Ahigh-spin Fe2+) + (1 × Aintermediate-spin Fe2+) + (5/2 × Ahigh-spin Fe3+)]/ΣA

Badro et al. 2004

Li et al. 2004

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Heated DAC Mössbauer spectroscopyHeated DAC Mössbauer spectroscopy

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Heated DAC nuclear forward scatteringHeated DAC nuclear forward scattering

diamond anvil cell

externalheating

CCD camera

ID18, ESRF

diamond anvil cell

externalheating

CCD camera

ID18, ESRF

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Pressure-temperature pathsPressure-temperature paths

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Spectra at high P,TSpectra at high P,T

55 GPa 800 K

Mössbauer spectroscopy

Fe2+ intermediate spin

62 GPa 1000 K

Nuclear forward scattering

Fe2+ intermediate spin

→ Intermediate spin stable at higher T

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

Effect of AlEffect of Al3+3+ and Fe and Fe3+3+ on spin transition on spin transitionMg0.86Fe0.14Si0.98Al0.02O3

• 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

Spin number variation with P,TSpin number variation with P,T

Sturhahn et al. 2005

Fe0.12Mg0.88SiO3

C. McCammon: Intermediate spin Fe2+ in lower mantle perovskite

SummarySummary

• 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