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Title: Time-Resolved Structural Analysis of K- and Ba-Exchange Reactions in Synthetic Na-birnessite using Synchrotron X-ray Diffraction

Abstract

Time-resolved Rietveld refinements using synchrotron X-ray diffraction (XRD) have documented real-time changes in unit-cell parameters in response to cation substitution in synthetic Na-birnessite. Potassium- and Ba-birnessite, like Na-birnessite, were found to have triclinic symmetry. Rietveld analyses of the XRD patterns for K- and Ba-exchanged birnessite revealed decreases in the a, c, and {beta} unit-cell parameters, with a decrease of 1.7 and 0.5%, respectively, in unit-cell volume relative to Na-birnessite. Fourier electron difference syntheses revealed that the changes in the configuration of the interlayer species, and the charge, size, and hydration of the substituting cations, serve as the primary controls on changes in unit-cell parameters. Split electron density maxima with centers at (0 0 0.5) were present for Na, K, and Ba end-members; however, with increased substitution of K{sup +} for Na{sup +}, the axis connecting the split-site maxima rotated from an orientation parallel to the b-axis to along the a-axis. Substitution of Ba{sup 2+} for Na{sup +} did not result in rotation, but splitting of the interlayer site was more pronounced.

Authors:
; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929891
Report Number(s):
BNL-80473-2008-JA
Journal ID: ISSN 0003-004X; AMMIAY; TRN: US0806669
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: American Mineralogist; Journal Volume: 92
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; CATIONS; CONFIGURATION; ELECTRON DENSITY; ELECTRONS; HYDRATION; ORIENTATION; POTASSIUM; ROTATION; SIZE; SYMMETRY; SYNCHROTRON RADIATION; VOLUME; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Lopano,C., Heaney, P., Post, J., Hanson, J., and Komarneni, S. Time-Resolved Structural Analysis of K- and Ba-Exchange Reactions in Synthetic Na-birnessite using Synchrotron X-ray Diffraction. United States: N. p., 2007. Web. doi:10.2138/am.2007.2242.
Lopano,C., Heaney, P., Post, J., Hanson, J., & Komarneni, S. Time-Resolved Structural Analysis of K- and Ba-Exchange Reactions in Synthetic Na-birnessite using Synchrotron X-ray Diffraction. United States. doi:10.2138/am.2007.2242.
Lopano,C., Heaney, P., Post, J., Hanson, J., and Komarneni, S. Mon . "Time-Resolved Structural Analysis of K- and Ba-Exchange Reactions in Synthetic Na-birnessite using Synchrotron X-ray Diffraction". United States. doi:10.2138/am.2007.2242.
@article{osti_929891,
title = {Time-Resolved Structural Analysis of K- and Ba-Exchange Reactions in Synthetic Na-birnessite using Synchrotron X-ray Diffraction},
author = {Lopano,C. and Heaney, P. and Post, J. and Hanson, J. and Komarneni, S.},
abstractNote = {Time-resolved Rietveld refinements using synchrotron X-ray diffraction (XRD) have documented real-time changes in unit-cell parameters in response to cation substitution in synthetic Na-birnessite. Potassium- and Ba-birnessite, like Na-birnessite, were found to have triclinic symmetry. Rietveld analyses of the XRD patterns for K- and Ba-exchanged birnessite revealed decreases in the a, c, and {beta} unit-cell parameters, with a decrease of 1.7 and 0.5%, respectively, in unit-cell volume relative to Na-birnessite. Fourier electron difference syntheses revealed that the changes in the configuration of the interlayer species, and the charge, size, and hydration of the substituting cations, serve as the primary controls on changes in unit-cell parameters. Split electron density maxima with centers at (0 0 0.5) were present for Na, K, and Ba end-members; however, with increased substitution of K{sup +} for Na{sup +}, the axis connecting the split-site maxima rotated from an orientation parallel to the b-axis to along the a-axis. Substitution of Ba{sup 2+} for Na{sup +} did not result in rotation, but splitting of the interlayer site was more pronounced.},
doi = {10.2138/am.2007.2242},
journal = {American Mineralogist},
number = ,
volume = 92,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}