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Phase transitions of BaCO3 at high pressures

Published online by Cambridge University Press:  05 July 2018

S. Ono*
Affiliation:
Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
J. P. Brodholt
Affiliation:
Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
G. D. Price
Affiliation:
Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
*

Abstract

First-principles simulations and high-pressure experiments were used to study the stability of BaCO3 carbonates at high pressures. Witherite, which is orthorhombic and isotypic with CaCO3 aragonite, is stable at ambient conditions. As pressure increases, BaCO3 transforms from witherite to an orthorhombic post-aragonite structure at 8 GPa. The calculated bulk modulus of the post-aragonite structure is 60.7 GPa, which is slightly less than that from experiments. This structure shows an axial anisotropicc ompressibility and the a axis intersects with the c axis at 70 GPa, which implies that the pressure-induced phase transition reported in previous experimental study is misidentified. Although a pyroxene-like structure is stable in Mg- and Ca-carbonates at pressures >100 GPa, our simulations showed that this structure does not appear in BaCO3.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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