Structural relaxation in the MnCO3-CaCo3 solid solution: A Mn K-edge EXAFS study

Young Jae Lee, R. J. Reeder, R. W. Wenskus, E. J. Elzinga

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Abstract

Mn K-edge EXAFS spectroscopy of solid-solution samples encompassing the complete MnCO3-CaCO3 series shows that first-shell Mn-O distances deviate little from the 2.19-Å distance observed in pure MnCO3. Very slight lengthening is observed only in the limiting case of dilute Mn(II) calcite solid solutions, where the Mn-O distance is 2.21 Å. The observed nearly complete structural relaxation and the composition independence of the Mn-O distance are consistent with the Pauling model behavior of solid solutions, and agree with previous studies showing a high degree of relaxation around hetero-sized substituents in the calcite structure. Strain occurs through bond bending, which is facilitated by the exclusively corner-sharing topology of calcite. Observed distances from Mn to more distant neighbors show significant variation across the solid-solution series that resembles Vegard's law-type behavior but reflects averaging. The high degree of relaxation suggests modest enthalpies of mixing in the solution, consistent with calorimetric studies.

Original languageEnglish
Pages (from-to)585-594
Number of pages10
JournalPhysics and Chemistry of Minerals
Volume29
Issue number9
DOIs
Publication statusPublished - 2002 Oct 1
Externally publishedYes

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Keywords

  • Calcite
  • EXAFS
  • Impurities
  • Relaxation
  • Rhodochrosite
  • Solid solutions

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Materials Science(all)

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