Dresden 2009 – scientific programme
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DF: Fachverband Dielektrische Festkörper
DF 12: Poster II
DF 12.9: Poster
Wednesday, March 25, 2009, 09:30–12:30, P5
Site-selective determination of coordination symmetries
by anisotropic anomalous X-ray scattering
— •M. Zschornak1,2, T. Leisegang1, H. Stöcker1, T. Weißbach1, S. Gemming2, and D.C. Meyer1 — 1Institute of Structural Physics, TU-Dresden, 01062 Dresden, Germany — 2Institute of Ion Beam Physics and Materials Research, FZ Dresden-Rossendorf, 01328 Dresden, Germany
Based on an experiment of Kirfel and Petcov on rutile (136) P42/mnm, which verified anisotropic anomalous scattering (AAS) by measuring ’Forbidden Reflection near Edge Diffraction’ (FRED) at an energy of 4985eV, we aimed to extend the results with allowed reflections to extract more tensor symmetries of the Ti scattering factor tensor fij. Furthermore we intended to study possible restrictions for atomic site occupation of unknown structures in an identified space group due to these local symmetry relations exemplary for this model structure. The rutile samples investigated were 10x10x1mm3 wafers in (001), (110) and (111) orientation and Ψ-scans were measured for the reflections 001, 220, 110 and 111. Ti occupies Wyckoff site 2a, its tensor symmetry must follow the local symmetry m.mm leaving 3 complex elements f11, f12, f33. The measured data show clear evidence of AAS and the 001 FRED and 111 intensities could be fitted to obtain f′12 and f″12. Since f13 and f23 were refined to zero, the positioning of Ti in the unit cell would by inverse symmetry arguments only be consistent with respect to site symmetry on Wyckoff sites a, b, e, f, g (out of k).