Journal
AMERICAN MINERALOGIST
Volume 94, Issue 5-6, Pages 666-675Publisher
MINERALOGICAL SOC AMER
DOI: 10.2138/am.2009.3120
Keywords
Apatite; hydroxylapatite; johnbaumite; arsenic; arsenate; NMR; EXAFS
Categories
Funding
- Korean Government [KRF-2007-331-C00250]
- Center for Environmental Molecular Science (NSF) [CHE-0221934]
- U.S. Department of Energy, Office of Science
- Office of Basic Energy Sciences [DE-AC02-980110886]
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Arsenate (As5+) substitution in the hydroxylapatite structure was examined using a combination of crystallographic and spectroscopic techniques. Samples of hydroxylapatite, the As5+-substituted analog (synthetic johnbaumite), and five intermediate compositions were synthesized from solution. Synchrotron X-ray diffraction data show that all samples are single-phase, confirming complete substitution. No evidence is found for lowering of symmetry below P6(3)/m. Rietveld structure refinements show progressive expansion of the unit cell with increasing As Substitution. which call be accounted for primarily by an average expansion of the tetrahedral site. Sizes of Ca polyhedra show little variation as a result of As substitution. NMR results show no evidence for local clustering of PO4 tetrahedra. EXAFS confirms that the size of As-centered tetrahedra remains constant across the solid-solution series.
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