Structural Study of Biotic and Abiotic Poorly-crystalline Manganese Oxides Using Atomic Pair Distribution Function Analysis
Manganese (Mn) oxides are among the most reactive natural minerals and play an important role in elemental cycling in oceanic and terrestrial environments. A large portion of naturally-occurring Mn oxides tend to be poorly-crystalline and/or nanocrystalline, with not fully resolved crystal structures. In this study, the crystal structures of their synthetic analogs including acid birnessite (AcidBir), {delta}-MnO{sub 2}, polymeric MnO{sub 2} (PolyMnO{sub 2}) and a bacteriogenic Mn oxide (BioMnO{sub x}), have been revealed using atomic pair distribution function (PDF) analysis. Results unambiguously verify that these Mn oxides are layered materials. The best models that accurately allow simulation of pair distribution functions (PDFs) belong to the monoclinic C12/m1 space group with a disk-like shape. The single MnO{sub 6} layers in the average structures deviate significantly from hexagonal symmetry, in contrast to the results of previous studies based on X-ray diffraction analysis in reciprocal space. Manganese occupancies in MnO{sub 6} layers are estimated to be 0.936, 0.847, 0.930 and 0.935, for AcidBir, BioMnO{sub x}, {delta}-MnO{sub 2} and PolyMnO{sub 2}, respectively; however, occupancies of interlayer cations and water molecules cannot be accurately determined using the models in this study. The coherent scattering domains (CSDs) of PolyMnO{sub 2}, {delta}-MnO{sub 2} and BioMnO{sub x} are at the nanometer scale, comprising one to three MnO{sub 6} layers stacked with a high disorder in the crystallographic c-axis direction. Overall, the results of this study advance our understanding of the mineralogy of Mn oxide minerals in the environment.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- USDOE SC OFFICE OF SCIENCE (SC)
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1045892
- Report Number(s):
- BNL-97166-2012-JA; GCACAK; R&D Project: PO-011; PO-010; KC0202010; TRN: US1203686
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 81; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CATIONS
COHERENT SCATTERING
CRYSTAL STRUCTURE
DISTRIBUTION FUNCTIONS
MANGANESE
MANGANESE OXIDES
MINERALOGY
OXIDE MINERALS
OXIDES
SHAPE
SIMULATION
SPACE GROUPS
SYMMETRY
WATER
X-RAY DIFFRACTION
nanoparticles and nanostructures
mass spectrometry
photoluminescence excitation spectra