College Park, Maryland June 6 - 10 , 2004 |
M2-C1 (10:30 AM): Prospects for Single Crystal Diffuse Scattering with Elastic Discrimination (Invited)
R. Osborn, S. Rosenkranz (Materials Science Division, Argonne National Laboratory)
There is growing interest in understanding complex materials in which disorder, and the nanoscale self-organization associated with it, plays an important role in their bulk properties. Examples of disorder in crystalline matrices include polaronic disorder in magnetoresistive oxides, stripe disorder in superconducting cuprates, nanodomains in ferroelectric relaxors, defect correlations in fast-ion conductors, rotational disorder in molecular solids and intercalation compounds, adsorption in microporous frameworks, and quasicrystals. Coherent diffuse scattering from single crystals, using either neutrons or x-rays, is the most powerful probe of such complex disorder. It is the only technique that can be used to determine both the local distortions around a point defect and the length scale and morphology of defect-defect correlations, i.e., the tendency for defects to cluster or self-assemble into nanoscale structures. Nevertheless, there are formidable technical difficulties both in obtaining reliable diffuse scattering data and in using it to construct models of defect structures. White-beam pulsed neutron instruments provide efficient access to the large volumes of reciprocal space that are required to model disorder accurately. However, they accomplish this without energy analysis so that static diffuse scattering is contaminated by inelastic scattering from vibrational and other dynamic processes in the sample. At present, there is no way to eliminate this inelastic signal without monochromating the incident or scattered beams, which results in a substantial loss of intensity. A proposed instrument, named Corelli, solves this problem by combining the high-efficiency of white-beam Laue diffraction with energy discrimination produced by the use of statistical choppers. The limitations of the cross–correlation method, by which the intrinsic scattering law is reconstructed from the modulated data, and the reasons for its effectiveness in this context will be discussed.
This work was performed under the support of the US Department of Energy,Office of Science, under contract no. W-31-109-ENG-38.
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