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Increasing accuracy in powder diffraction

Vendredi 7 mars 2014 10:00 - Duree : 1 heure
Lieu : Room 500-501, Central Building, ESRF - 6 Rue Jules Horowitz - Grenoble

Orateur : Oksana MAGDYSYUK (Max Planck Institute for Solid State Research - Germany)

One of the important problems in structural analysis of powder diffraction data is increasing accuracy of the reconstructed electron density map. Conventional Fourier synthesis strongly depends on the resolution of experimental powder diffraction data. To overcome the limitations of Fourier synthesis, the maximum entropy method (MEM) was introduced in the field of crystallography. The MEM allows the maximization of the information extracted from intrinsically limited and/or noisy experimental X–ray powder diffraction data. It has been demonstrated that MEM can be successfully used with powder diffraction data for localization of missing atoms with high occupancies in incomplete crystal structures (1, 2), for revealing the true nature of structural disorder (3, 4) and for determination of integrated atomic charges (5). On the other hand, the capability of the MEM to locate missing atoms with low occupancies is not fully investigated. This holds in particular true in case of commonly used high-resolution laboratory X-ray powder diffraction data. In the present study, the MEM was used to locate small amount of intercalated metal atoms (Cu, Ni, Zn) in incomplete crystal structures of apatites, and to determine their electron density distribution (6). Also the intercalation of noble gas atoms in metal-organic framework CPO-27, ZIF-8, and MFU-4l was investigated by conventional powder diffraction methods and by MEM (7). The quality of the analysis of in situ powder diffraction investigations of structural phase transitions can be improved by the application of parametric Rietveld refinement (8), and by the analysis of the crystal structure in terms of the distortion of a parent high-symmetry structure (9). Parametric refinement allows the application of a realistic physical model during refinement. Thus, testing of different models describing the investigated physical process can be performed with increased accuracy. In the present work, parametric Rietveld refinement and parametric Le Bail whole powder pattern fitting were successfully applied for the analysis of different mathematical models of coupling between strain and order parameter for the high temperature structural phase transitions in LuF[SeO3] and Sr2CoOsO6 (10). [1] Kitaura, R. ; Kitagawa, S. ; Kubota, Y. ; Kobayashi, T. C. ; Kindo, K. ; Mita, Y. ; Matsuo, A. ; Kobayashi, M. ; Chang, H. ; Ozawa, T. C. ; Suzuki, M. ; Sakata, M. and Takata, M. (2002). Science. 298, 2358. [2] Matsuda, R. ; Kitaura, R. ; Kitagawa, S. ; Kubota, Y. ; Belosludov, R. V. ; Kobayashi, T. C. ; Sakamoto, H. ; Chiba, T. ; Takata, M. ; Kawazoe, Y. and Mita, Y. (2005). Nature. 436, 238. [3] Dinnebier, R. E. ; Schneider, M. ; van Smaalen, S. ; Olbrich, F. and Behrens, U. (1999). Acta Cryst. B55, 35. [4] Samy, A. ; Dinnebier, R. E. ; van Smaalen, S. and Jansen, M. (2010). Acta Cryst. B66, 184. [5] Buchter, F. ; Lodziana, Z. ; Remhof, A. ; Mauron, Ph. ; Friedrichs, O. ; Borgschulte, A. ; Züttel, A. ; Filinchuk, Y. and Palatinus, L. (2011). Phys. Rev. B. 86, 064107. [6] Magdysyuk, O.V. ; Dinnebier ; R.E. ; van Smaalen, S. ; Zykin, M.A. ; Kazin, P.E. ; Jansen, M. (2012). Z. Kristallog. 227, 321. [7] Soleimani-Dorcheh, A. ; Dinnebier, R.E. ; Kuc, A. ; Magdysyuk, O.V. ; Adams, F. ; Denysenko, D. ; Heine, Th. ; Volkmer, D. ; Donner, W. ; Hirscher, M. (2012). PCCP. 14, 12892. [8] Stinton, G.W. ; Evans, J.S.O. (2007), J. Appl. Cryst. 40, 87. [9] Campbell, B.J. ; Stokes, H.T. ; Tanner, D.E. ; Hatch, D.M. (2006). J. Appl. Cryst. 39, 607. [10] Magdysyuk, O.V. ; Mueller, M. ; Dinnebier ; R.E. ; Lipp, C. ; Schleid, Th. (2014) (accepted to J. Appl. Cryst.)

Contact : isabelle.combe@esrf.fr

Discipline évènement : (Physique)
Entité organisatrice : (ESRF)
Nature évènement : (Séminaire)
Evènement répétitif : (Séminaire ESRF)
Site de l'évènement : Polygone scientifique

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