Physics and Chemistry of Minerals

, Volume 37, Issue 5, pp 265–282

Equation of state and pressure-induced structural changes in mirabilite (Na2SO4·10H2O) determined from ab initio density functional theory calculations

Authors

  • Helen E. A. Brand
    • Department of Earth SciencesUniversity College London
    • Center for Planetary Sciences at UCL/Birkbeck
    • CSIRO Minerals
    • Department of Earth SciencesUniversity College London
    • Center for Planetary Sciences at UCL/Birkbeck
  • Ian G. Wood
    • Department of Earth SciencesUniversity College London
    • Center for Planetary Sciences at UCL/Birkbeck
  • Lidunka Vočadlo
    • Department of Earth SciencesUniversity College London
    • Center for Planetary Sciences at UCL/Birkbeck
Original Paper

DOI: 10.1007/s00269-009-0331-1

Cite this article as:
Brand, H.E.A., Fortes, A.D., Wood, I.G. et al. Phys Chem Minerals (2010) 37: 265. doi:10.1007/s00269-009-0331-1

Abstract

We have carried out ab initio calculations using density functional theory to determine the bulk elastic properties of mirabilite, Na2SO4·10H2O, and to obtain information on structural trends caused by the application of high pressure up to ~60 GPa. We have found that there are substantial isosymmetric discontinuous structural re-organisations at ~7.7 and ~20 GPa caused by changes in the manner in which the sodium cations are coordinated by water molecules. The low-pressure and intermediate-pressure phases both have sodium in sixfold coordination but in the high-pressure phase the coordination changes from sixfold to sevenfold. These coordination changes force a re-arrangement of the hydrogen-bond network in the crystal. The trend is towards a reduction in the number of hydrogen bonds donated to the sulphate group (from twelve down to six over the range 0–60 GPa) and an increase in hydrogen bonding amongst the Na-coordinated water molecules and the two interstitial water molecules. Ultimately, we observe proton transfers from the interstitial waters (forming OH ions) to two of the Na-coordinated waters (forming a pair of H3O+ ions). The equation of state in the athermal limit of the low-pressure phase of mirabilite, parameterised by fitting an integrated form of the third-order Birch-Murnaghan expression to the calculated energy as a function of unit-cell volume, yields the zero-pressure unit-cell volume, V0 = 1468.6(9) Å3, the incompressibility, K0 = 22.21(9) GPa, and the first pressure derivative K0′ = (∂K/∂P)0 = 5.6(1).

Keywords

MirabiliteAb initio calculationsIncompressibilitySalt hydrates

Supplementary material

269_2009_331_MOESM1_ESM.doc (210 kb)
Supplementary material 1 (DOC 209 kb)
269_2009_331_MOESM2_ESM.doc (3.6 mb)
Supplementary material 2 (DOC 3.59 mb)

Copyright information

© Springer-Verlag 2009