Structure of Cs[NbWO] analysed by focal-series reconstruction and crystallographic image processing
by Juri Barthel, Thomas E. Weirich, Gerhard Cox, Hartmut Hibst, and Andreas Thust
The structure of the oxygen sub-lattice in Cs0.5[Nb2.5W2.5O14] has been investigated for the first time by advanced electron-optical methods. Since the material resembles the crystal structure of the so-called M1 phase of Mo-V-Nb-Te-O, which is the best catalyst for the selective oxidation of propane to acrylic acid, the structure analysis of the oxygen sub-lattice can contribute substantially to a better understanding of this catalytic process.
In the present study, the so far only partially known structure of the complex metal oxide Cs0.5[Nb2.5W2.5O14] has been investigated by combining modern methods of high-resolution transmission electron microscopy with crystallographic image processing techniques.
Average atom positions in the añb plane are determined from the phase of the exit-plane wave function, which was numerically reconstructed from a focal series of spherical-aberration-corrected electron micrographs. The experimentally determined atom positions agree well with a structure model obtained by first-principles calculations for the underlying M5O14 (M = Nb, W) framework. Moreover, several deviations from the periodic structure, which may influence the catalytic properties of the structurally similar M1 phase, have been observed. The obtained results demonstrate that aberration-corrected high-resolution transmission electron microscopy is a reliable alternative for the analysis of periodic structures, in particular when traditional methods for crystallographic structure determination like XRD or neutron diffraction cannot be applied.
Juri Barthel, Thomas E. Weirich, Gerhard Cox, Hartmut Hibst, and Andreas Thust: Structure of Cs[NbWO] analysed by focal-series reconstruction and crystallographic image processing, Acta Materialia 58 (2010) 3764-3772.