| Autor: |
Steciuk G; Department of Structure Analysis, Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, Prague 8 182 21, Czech Republic., Kiefer B; Department of Physics, New Mexico State University, Las Cruces, New Mexico 88003, United States., Hornfeck W; Department of Structure Analysis, Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, Prague 8 182 21, Czech Republic., Kasatkin AV; Fersman Mineralogical Museum of Russian Academy of Sciences, Leninsky Prospekt 18-2, 119071 Moscow, Russia., Plášil J; Department of Structure Analysis, Institute of Physics, Czech Academy of Sciences, Na Slovance 1999/2, Prague 8 182 21, Czech Republic. |
| Abstrakt: |
Sedovite, U 4+ (Mo 6+ O 4 ) 2 · n H 2 O, is reported as being one of the earliest supergene minerals formed of the secondary zone. The difficulty of isolating enough pure material limits studies to techniques that can access the nanoscale combined with theoretical analyses. The crystal structure of sedovite has been solved and refined using the dynamical approach from three-dimensional electron diffraction data collected on natural nanocrystals found among iriginite. At 100 K, sedovite is monoclinic a ≈ 6.96 Å, b ≈ 9.07 Å, c ≈ 12.27 Å, and V ≈ 775 Å 3 with space group C 2/ c . The microporous structure presents a characteristic framework built from uranium polyhedra and disordered Mo pyramids creating pore hosting water molecules. To confirm the formula U 4+ (Mo 6+ O 4 ) 2 · n H 2 O, the possible presence of a hydroxyl group that would promote Mo 5+ was tested with density functional theory (DFT) computations at the ambient temperature. DFT predicts that sedovite is a ferromagnetic insulator with a fundamental bandgap of E g ∼ 1.7 eV with its chemical and physical properties dominated by U 4+ rather than Mo 6+ . The structural complexity, I G,tot , of sedovite was evaluated in order to get indirect information about the missing formation conditions. |
