intermediate spin fe 2+ in lower mantle perovskite
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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