Journal
EARTH AND PLANETARY SCIENCE LETTERS
Volume 224, Issue 3-4, Pages 241-248Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2004.05.017
Keywords
post-perovskite; MgSiO3; first principle; core-mantle boundary; D '' layer
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A new polymorph of MgSiO3 more stable than the Pbnm-perovskite phase has been identified by first-principles computations. It has the CaIrO3 structure with Cmcm symmetry and consists of SiO3 layers intercalated by eightfold-coordinated Mg ions. High-temperature calculations within the quasiharmonic approximation give a volume change of similar to 1.5% and a Clapeyron slope of similar to 7.5 +/- 0.3 MPa/K at similar to 2750 K and similar to 125 GPa. These pressure-temperature (P-T) conditions are close to those in which a phase transition in MgSiO3-perovskite has been observed by in situ angle dispersive X-ray diffraction measurements. This transition appears to be associated with the W discontinuity. (C) 2004 Elsevier B.V All rights reserved.
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