Stability and equation of state of post-aragonite BaCO3

Joshua P. Townsend, Yun Yuan Chang, Xiaoting Lou, Miguel Merino, Scott J. Kirklin, Jeff W. Doak, Ahmed Issa, Chris Wolverton, Sergey N. Tkachev, Przemyslaw Dera, Steven D. Jacobsen

Research output: Contribution to journalArticlepeer-review

14 Scopus citations

Abstract

At ambient conditions, witherite is the stable form of BaCO3 and has the aragonite structure with space group Pmcn. Above ~10 GPa, BaCO3 adopts a post-aragonite structure with space group Pmmn. High-pressure and high-temperature synchrotron X-ray diffraction experiments were used to study the stability and equation of state of post-aragonite BaCO3, which remained stable to the highest experimental P-T conditions of 150 GPa and 2,000 K. We obtained a bulk modulus K0 = 88(2) GPa with K′ = 4.8(3) and V0 = 128.1(5) Å3 using a third-order Birch-Murnaghan fit to the 300 K experimental data. We also carried out density functional theory (DFT) calculations of enthalpy (H) of two structures of BaCO3 relative to the enthalpy of the post-aragonite phase. In agreement with previous studies and the current experiments, the calculations show aragonite to post-aragonite phase transitions at ~8 GPa. We also tested a potential high-pressure post-post-aragonite structure (space group C2221) featuring four-fold coordination of oxygen around carbon. In agreement with previous DFT studies, ΔH between the C2221 structure and post-aragonite (Pmmn) decreases with pressure, but the Pmmn structure remains energetically favorable to pressures greater than 200 GPa. We conclude that post-post-aragonite phase transformations of carbonates do not follow systematic trends observed for post-aragonite transitions governed solely by the ionic radii of their metal cations.

Original languageEnglish (US)
Pages (from-to)447-453
Number of pages7
JournalPhysics and Chemistry of Minerals
Volume40
Issue number5
DOIs
StatePublished - 2013

Keywords

  • BaCO
  • Carbonates
  • Equation of state
  • High pressure

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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