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Diffraction by disordered crystalline materials

By Jonathan L Eads

Abstract

X-ray diffraction from crystalline materials is influenced by both the conformation and the packing of the constituent molecules. In a regular crystal, the molecules pack on a periodic lattice. Analysis of molecular structures using X-ray crystallography is usually based on such specimens. However, many materials form only partially ordered, or disordered, crystals. This thesis is concerned with models of disordered crystalline materials and their diffraction characteristics. Several models of lattice disorder in one and two dimensions are examined. The statistics and diffraction by one-dimensional paracrystals and perturbed lattices are compared. Diffraction by the two-dimensional ideal paracrystal is studied in detail. The spiral paracrystal model is used to examine the observed crystallite size - disorder relationship for disordered crystals, and the statistics and diffraction by the spiral paracrystal are also examined. A method is developed for including the effects of disorder in the determination of polymer structures from X-ray fiber diffraction data. This method is applied to data from a screw-disordered polynucleotide fiber

Topics: Condensation|Biophysics|Materials science
Publisher: 'Purdue University (bepress)'
Year: 2001
OAI identifier: oai:docs.lib.purdue.edu:dissertations-4360
Provided by: Purdue E-Pubs
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