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 language | English |
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Pages (from-to) | 585-594 |
Number of pages | 10 |
Journal | Physics and Chemistry of Minerals |
Volume | 29 |
Issue number | 9 |
DOIs | |
Publication status | Published - 2002 Oct |
Externally published | Yes |
Keywords
- Calcite
- EXAFS
- Impurities
- Relaxation
- Rhodochrosite
- Solid solutions
ASJC Scopus subject areas
- Materials Science(all)
- Geochemistry and Petrology