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Science 26 May 2006:
Vol. 312. no. 5777, pp. 1205 - 1208
DOI: 10.1126/science.1125622
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Reports

Reduced Radiative Conductivity of Low-Spin (Mg,Fe)O in the Lower Mantle

Alexander F. Goncharov,* Viktor V. Struzhkin, Steven D. Jacobsen{dagger}

Optical absorption spectra have been measured at pressures up to 80 gigapascals (GPa) for the lower-mantle oxide magnesiowüstite (Mg,Fe)O. Upon reaching the high-spin to low-spin transition of Fe2+ at about 60 GPa, we observed enhanced absorption in the mid- and near-infrared spectral range, whereas absorption in the visible-ultraviolet was reduced. The observed changes in absorption are in contrast to prediction and are attributed to d-d orbital charge transfer in the Fe2+ ion. The results indicate that low-spin (Mg,Fe)O will exhibit lower radiative thermal conductivity than high-spin (Mg,Fe)O, which needs to be considered in future geodynamic models of convection and plume stabilization in the lower mantle.

Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA.

{dagger} Present address: Department of Geological Sciences, Northwestern University, Evanston, IL 60208, USA.

* To whom correspondence should be addressed. E-mail: goncharov{at}gl.ciw.edu

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