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Ab Initio Investigation of the High Pressure Elasticity of Mg2SiO4 Forsterite and Ringwoodite

Published online by Cambridge University Press:  10 February 2011

Lars Stixrude ,
R. M. Wentzcovitch ,
C. Da Silva  and
B. Kiefer
Lars Stixrude
Affiliation:
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109–1063
R. M. Wentzcovitch
Affiliation:
Dept. of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
C. Da Silva
Affiliation:
Dept. of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
B. Kiefer
Affiliation:
Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109–1063
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Abstract

We discuss the behavior of two minerals of the same composition, Mg2SiO4 but different structures: forsterite and ringwoodite. Ab initio plane-wave pseudopotential results are discussed in terms of the full elastic constant tensors of these phases and their elastic anisotropy. The structures of the two minerals, based on pseudo-hep and pseudo-fee packing of oxygens, respectively, show very different behavior at high pressure. While the elastic anisotropy of olivine depends weakly on pressure between 0 and 25 GPa, the anisotropy of ringwoodite decreases with pressure initially, vanishing at 17 GPa before increasing again at higher pressure. This unusual behavior is understood in terms of a change of sign of the combination of elastic constants c2+2c44-c11, and a resulting interchange of fast and slow directions of acoustic wave propagation. To gain insight into the origin of their elastic behavior, the ab initio results are compared with a simple model based on the O sub-lattice.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 499: Symposium DD – High Pressure Materials Research , 1997 , 15
Copyright
Copyright © Materials Research Society 1998

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References

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