Spin state of ferric iron in MgSiO{sub 3} perovskite and its effect on elastic properties.

Journal Article · Fri Jan 15 04:00:00 EST 2010 · Earth Planet. Sci. Lett.

DOI:https://doi.org/10.1016/j.epsl.2009.10.029· OSTI ID:973026

Catalli, K; Shim, S H; Prakapenka, V B; Zhao, J; Sturhahn, W; Chow, P; Xiao, Y; Liu, H; Cynn, H; Evans, W J

Recent studies have indicated that a significant amount of iron in MgSiO{sub 3} perovskite (Pv) is Fe{sup 3+} (Fe{sup 3+}/{Sigma}Fe = 10-60%) due to crystal chemistry effects at high pressure (P) and that Fe{sup 3+} is more likely than Fe{sup 2+} to undergo a high-spin (HS) to low-spin (LS) transition in Pv in the mantle. We have measured synchrotron Moessbauer spectroscopy (SMS), X-ray emission spectroscopy (XES), and X-ray diffraction (XRD) of Pv with all iron in Fe{sup 3+} in the laser-heated diamond-anvil cell to over 100 GPa. Fe{sup 3+} increases the anisotropy of the Pv unit cell, whereas Fe{sup 2+} decreases it. In Pv synthesized above 50 GPa, Fe{sup 3+} enters into both the dodecahedral (A) and octahedral (B) sites approximately equally, suggesting charge coupled substitution. Combining SMS and XES, we found that the LS population in the B site gradually increases with pressure up to 50-60 GPa where all Fe{sup 3+} in the B site becomes LS, while Fe{sup 3+} in the A site remains HS to at least 136 GPa. Fe{sup 3+} makes Pv more compressible than Mg-endmember below 50 GPa because of the gradual spin transition in the B site together with lattice compression. The completion of the spin transition at 50-60 GPa increases bulk modulus with no associated change in density. This elasticity change can be a useful seismic probe for investigating compositional heterogeneities associated with Fe{sup 3+}.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: NSF; SC; State of Illinois
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 973026
• Report Number(s): ANL/XSD/JA-63528
• Journal Information: Earth Planet. Sci. Lett., Journal Name: Earth Planet. Sci. Lett. Journal Issue: 1-2 ; Jan. 15, 2010 Vol. 289; ISSN 0012-821X; ISSN EPSLA2
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

43 PARTICLE ACCELERATORS
ANISOTROPY
CHEMISTRY
COMPRESSION
ELASTICITY
EMISSION SPECTROSCOPY
IRON
MOESSBAUER EFFECT
PEROVSKITE
PROBES
SPIN
SYNCHROTRONS
X-RAY DIFFRACTION