Neutron diffraction study of hydrogen in birnessite structures

Jeffrey E. Post, Peter J. Heaney, Yunchul Cho

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

The positions of hydrogen (deuterium) cations within the interlayer of synthetic Na-and K-birnessite samples have been determined for the first time using Rietveld analysis and Fourier difference syntheses, from time-of-flight powder neutron diffraction data. This study revealed that two symmetry-related D(H) positions are located ∼1 Å above and below the midpoint between the split O interlayer sites in Na-birnessite. This result confirms our earlier interpretation that the split interlayer sites include O atoms from two symmetrically equivalent H2O molecules. These molecules are oriented 180° to each other, and they are pivoted about a single set of H(D) atoms positions. The interlayer H2O molecules in K-birnessite are oriented such that one of the H(D) atoms is pointed approximately toward the Mn octahedral layer O atoms and the other is directed approximately within the net of interlayer K/O sites. In K-birnessite, six K-Ooct distances are shorter than 3.35 Å, compared with only two Na-Ooct bond lengths in Na-birnessite, suggesting that K cations are more tightly bonded to the octahedral O atoms than are Na cations.

Original languageEnglish (US)
Pages (from-to)534-540
Number of pages7
JournalAmerican Mineralogist
Volume96
Issue number4
DOIs
StatePublished - Apr 1 2011

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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