Thermophysical properties of the α-β-γ polymorphs of Mg2SiO4: A computational study

G. Ottonello, B. Civalleri, J. Ganguly, M. Vetuschi Zuccolini, Y. Noel

Research output: Contribution to journalArticle

38 Scopus citations

Abstract

Thermophysical properties of the various polymorphs (i.e. α-, β- and γ) of Mg2SiO4 were computed with the CRYSTAL06 code within the framework of CO-LCAO-GTF approach by using the hybrid B3LYP density functional method. Potential wells were calculated through a symmetry preserving, variable cell-shape structure relaxation procedure. Vibrational frequencies were computed at the long-wavelength limit corresponding to the center of the Brillouin zone (k → 0). Thermodynamic properties were estimated through a semiclassical approach that combines B3LYP vibrational frequencies for optic modes and the Kieffer's model for the dispersion relation of acoustic modes. All computed values except volume (i.e. electronic energy, zero point energy, optical vibrational modes, thermal corrections to internal energy, standard state enthalpy and Gibbs free energy of reaction, bulk modulus and its P and T derivatives, entropy, CV, CP) are consistent with available experimental data and/or reasonable estimates. Volumes are slightly overestimated relative to those determined directly by X-ray diffraction. A set of optimized volumetric properties that are consistent with the other semiclassical properties of the phases α, β and γ have been derived by optimization procedure such that the calculated boundaries for the α/β and α/β equilibria have the best overall agreement with the experimental data for these transitions.

Original languageEnglish (US)
Pages (from-to)87-106
Number of pages20
JournalPhysics and Chemistry of Minerals
Volume36
Issue number2
DOIs
StatePublished - Jan 1 2009

Keywords

  • Forsterite
  • Polymorphic transitions
  • Ringwoodite
  • Thermodynamic properties
  • Wadsleyite

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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