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Science 16 July 2004:
Vol. 305. no. 5682, pp. 383 - 386
DOI: 10.1126/science.1098840
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Reports

Electronic Transitions in Perovskite: Possible Nonconvecting Layers in the Lower Mantle

James Badro,1* Jean-Pascal Rueff,2 György Vankó,3 Giulio Monaco,3 Guillaume Fiquet,1 François Guyot1

We measured the spin state of iron in magnesium silicate perovskite (Mg0.9,Fe0.1)SiO3 at high pressure and found two electronic transitions occurring at 70 gigapascals and at 120 gigapascals, corresponding to partial and full electron pairing in iron, respectively. The proportion of iron in the low spin state thus grows with depth, increasing the transparency of the mantle in the infrared region, with a maximum at pressures consistent with the D'' layer above the core-mantle boundary. The resulting increase in radiative thermal conductivity suggests the existence of nonconvecting layers in the lowermost mantle.

1 Laboratoire de Minéralogie Cristallographie de Paris (UMR CNRS 7590), Institut de Physique du Globe de Paris, Université Paris, 6 and 7, 4 Place Jussieu, 75252 Paris, France.
2 Laboratoire de Chimie Physique–Matière et Rayonnement (UMR CNRS 7614), Université Paris, 6 11 Rue Pierre et Marie Curie, 75231 Paris, France.
3 European Synchrotron Radiation Facility (ESRF), B.P. 220 F-38043 Grenoble CEDEX, France.

* To whom correspondence should be addressed. E-mail: james.badro{at}lmcp.jussieu.fr

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