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Phase transitions of BaCO₃ at high pressures

¹ Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK
² Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

^* E-mail: sono{at}jamstec.go.jp

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 anisotropic compressibility 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.

KEYWORDS: BaCO₃, phase transition, high pressure, ab initio calculation