Dresden 2014 – scientific programme
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KR: Fachgruppe Kristallographie
KR 8: Poster Crystallography
KR 8.1: Poster
Wednesday, April 2, 2014, 17:00–19:30, P4
Analyzing high pressure diffraction data of perovskites with parametric Rietveld refinement and rotational symmetry modes of a rigid body — •Martin Etter1, Melanie Müller1, Michael Hanfland2, and Robert E. Dinnebier1 — 1Max Planck Institut für Festkörperforschung, Stuttgart, Germany — 2European Synchrotron Radiation Facility (ESRF), Grenoble, France
The high pressure behavior of crystals can best be observed with X-ray or neutron diffraction methods, as these methods allow the application of least square iteration processes (e.g. Rietveld method) to refine parameters, which are directly connected with structural and/or magnetic changes within the crystal. A challenge of the investigation of diffraction patterns under high pressure is that the data quality often decreases after only a few GPa, which makes it difficult for a least square iteration process to find the correct minimum. For this reason, adequate structural models are needed in order to stabilize the refinement and to decrease the number of free parameters. Such models can be provided by the application of rigid bodies, symmetry modes or the recently developed method of rotational symmetry modes of a rigid body which combines the advantages of both. Additionally, these models can be parameterized, treating different data sets simultaneously with the application of physical equations as constraints, which leads to a further reduction of refined parameters. In order to illustrate the power of this new approach, sequential and parametric Rietveld refinements of a LaFeO3 perovskite investigated with synchrotron powder X-ray diffraction under high pressure were carried out.