Type of presentation: Poster

MS-14-P-3190 Local Imaging and Measuring of Distortions in the Oxygen Sub-Lattice of Complex Mixed Oxides

Lunkenbein T.1, Girgsdies F.1, Noack J.1, Trunschke A.1, Schlögl R.1, Willinger M. G.1
1Fritz-Haber-Institute of the Max-Planck-Society, Berlin, Germany
lunkenbein@fhi-berlin.mpg.de

“It would be very easy to make an analysis of any complicated chemical substance; all one would have to do would be to look at it and see where the atoms are. The only trouble is that the electron microscope is one hundred times too poor.” With this statement in his famous speech “There is plenty of room at the bottom” R. Feynman has already highlighted the future importance of transmission electron microscopes (TEMs) in 1959.

Nowadays modern Cs corrected TEMs are powerful enough to obtain point resolution below 50 pm.[1] However, direct imaging of light elements next to heavy elements remains complex. In probe corrected scanning transmission electron microscopy (STEM) recent developments tackle this challenge, resulting in the revival of the annular bright field (ABF) detector. In contrary to the contrast detected by the high angle annular dark field (HAADF) method, which is due to Rutherford scattering and proportional to Z2, the ABF detector is also sensitive to light elements.[2]

Using the ABF detector, we investigated orthorhombic (Mo,V) oxides crystallized in a structure analog to the M1 structure (ICSD no. 55097) of MoVTeNb oxide. The obtained micrographs were compared with Rietveld refined X-ray diffraction (XRD) data. Fig.1 shows an ABF image where the oxygen atoms brighten up. Furthermore we directly measured metal-oxygen bond angles and discussed the oxidation states of the metal centers.

Our results prove Feynman´s prediction. Seeing where the atoms are, generates in particular in heterogeneous catalysis a deeper understanding of the functionality of materials on the way towards tailor-made catalysts.

Refernces:

[1] a) R. Erni, M. D. Rossell, C. Kisielowski, U. Dahmen, Phys. Rev. Lett. 2009, 102, 096101; b) K. Takayanagi, S. Kim, S. Lee, Y. Oshima, T. Tanaka, Y. Tanishiro, H. Sawada, F. Hosokawa, T. Tomita, T. Kaneyama, Y. Kondo, J. Electron Microsc. 2011, 60, S239-S244.

[2] a) P. E. Batson, Nat Mater 2011, 10, 270-271; b) S. D. Findlay, N. Shibata, H. Sawada, E. Okunishi, Y. Kondo, Y. Ikuhara, Ultramicroscopy 2010, 110, 903-923.

The authors acknowledge Jeol and the Max-Planck-Society for help and financial support.

Fig. 1: (A) Atomic resolution ABF-STEM image of (Mo,V)Ox. The white rectangle displays the orthorhombic unit cell, which is in good agreement with the ABF image. Metal sites are partially highlighted with blue circles and oxygen sites are labeled with red circles. (B) Corresponding HAADF image of the same region.