P 56 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
XAS STUDY OF Mo DOPED TiO
2NANOPARTICLE MATERIALS
K. Schneider1,3∗, M. Sikora1, J. St¸epie´n1, K. Biernacka1, Cz. Kapusta1, D. Zajac2, K. Michalow-Mauke4, Th. Graule4, A. Vital4, K. Zakrzewska3, and M. Rekas5
1Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krak´ow, Poland
2Helmholtz-Zentrum Berlin f¨ur Materialien und Energie GmbH, Institute of Solar Fuels and Energy Storage Materials, Berlin
3Faculty of Electrical Engineering, Automatics, Computer Science and Electronics, AGH University of Science and Technology, Krak´ow, Poland
4EMPA, 129, Ueberlandstrasse, Duebendorf, Switzerland
5Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Krak´ow, Poland
Keywords: titanium dioxide, nanomaterials, XAS spectroscopy
∗e-mail : kryschna@agh.edu.pl
A XAS study of the Mo-doped TiO2 (0.4 and 1 at % Mo) nanoparticle materials at the K edges of molibdenum are presented. The materials were pre- pared with Flame Spray Synthesis (FSS) process by oxidation of metal-organics precursors. The mea- surements at the molybdenum K edge were carried out at the E4 beamline with the total fluorescence detection at room temperature (HASYLAB, DESY, Hamburg, Germany).
The Mo:K EXAFS functions presented in the Fig. 1 show a considerable decrease of the second- neighbour-shell peak with increasing Mo content, which corresponds to increased number of cation va- cancies. The Mo XANES spectra are very nearly the same, which indicates the same Mo oxidation state in both samples. A close similarity to the XANES spectrum of MoO3 indicates a Mo6+ state with a similar distribution of oxygen distances in the near- est neighbour shell, confirmed by simulations.
Figure 1 : XANES spectra on Mo:K edge for Mo-doped TiO2(0.5 at % Mo — solid line and 1 at % Mo — dashed line).
Figure 2 : Fourier transforms of the Mo:K edge EXAFS functions for Mo-doped TiO2 (0.5 at % Mo — solid line and 1 at % Mo — dashed line).
The EXAFS functions in the R space obtained from the Mo:K edge spectra are presented in the Fig. 2. The peak of the oxygen nearest neighbour shell is centered at 1.4 ˚A. The second peak, which is centered at 2.6 ˚A corresponding to the cations in the 2nd nearest neighbour shell is two times smaller in the sample with 1% Mo than for 0.5%
Mo. This corresponds to a two times smaller num- ber of cation nearest neighbours in the 1% Mo sam- ple, i.e to about 50% cation vacancies in the 2nd nearest neighbour shell of Mo ion. Having in mind that the number of cation neighbours in this shell corresponding to the anatase structure is 4 and in the rutile structure is 2 this would mean that the Mo ions in the 1% Mo sample have the local ionic environment characteristic for rutile. This is also confirmed by a slightly larger distance of the 1st oxygen neighbour shell in this sample.
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