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Poster De Conférence Année : 2023

Unraveling the structure of TlNbOx bronze oxide by atomic STEM and STEM-EDX

M. Aouine
T.-M.-N. Le
  • Fonction : Auteur
Y. Lefkir
  • Fonction : Auteur
S. Reynaud
  • Fonction : Auteur

Résumé

Several mild oxidation catalysts consist in metal (e.g. Bi, V) molybdates with a high-temperature bronze type structure. Targetted catalytic properties are the oxidation of propane to acrylic acid and the oxidative dehydrogenation of ethane. In the present work, new compounds were successfully synthesized by the microwave-assisted hydrothermal method, which exhibit catalytic properties comparable to those obtained with conventional techniques but more expensive in energy and much longer to elaborate. Among these new compounds, a new hexagonal niobate with a similar structure was obtained, thallium niobate Tl7Nb39O101, which to the best of our knowledge has not been detected before. Its relatively complex structure was determined by X-ray diffraction on the basis of precious information obtained by advanced transmission electron microscopy work, e.g. STEM imaging (300 kV FEI/TFS Titan ETEM, see figure 1a), aberration-corrected STEM imaging and STEM-EDX atomic mapping (200 kV JEOL Neo ARM equipped with a Centurio Large Angle SDD-EDS detector, fig. 1b). We have used the e-ABF images constructed by subtracting the BF signal (fig. 1c) to the ADF (fig. 1d) one [1]. An adequate restoration of the ADF image by optimizing the weighting factors of both e-ABF and BF images as: ADF’ = x BF + (1-x) e-ABF, allows to highlight both light (oxygen) and heavy (metal) atomic columns much more efficiently than in the ADF image directly acquired. A careful examination of these ADF’ images (fig. 1e) further reveals that the Tl-niobate exhibits a P3 symmetry which is not be visible in conventional (HA)ADF images such as shown in fig. 1a), which exhibits the 6-fold symmetry of the cationic sublattice. Accordingly, improved images were produced by applying the P3 symmetry to averaged unit cells in order to increase the signal-to-noise ratio. The result of this treatment is reported for the hexagonal motif in figure 1f. It is suggested that these bright-field type atomic images possibly reveal the location of required Nb interstitials cations insuring the electroneutrality of the solid. All these data are still under analysis in order to complete the structural investigation through a converging TEM / DRX Rietveld refinement approach [2]. References: [1] S.D. Findlay et al., Ultramicroscopy 136 (2014) 41. [2] Thanks are due to the CLYM (www.clym.fr) for the access to the microscopes.
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Dates et versions

hal-04158834 , version 1 (11-07-2023)

Identifiants

  • HAL Id : hal-04158834 , version 1

Citer

M. Aouine, T.-M.-N. Le, T. Epicier, Y. Lefkir, S. Reynaud, et al.. Unraveling the structure of TlNbOx bronze oxide by atomic STEM and STEM-EDX. 18ème Colloque de la SFµ, Jul 2023, Rouen, France. ⟨hal-04158834⟩
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