A Novel Approach to Discovering and Describing Planar Disorder in Layered Materials from their Diffraction Spectra

Nonlinear Dynamics and Complex Systems Seminar

University of Illinois

April 2004


Although an understanding of structure is well developed for crystalline materials, a similar understanding for the structure of disordered materials is largely lacking. For the special but important case of planar faulting, I introduce a novel technique for detecting and characterizing disordered stacking structure directly from X-ray diffraction spectra. Using computational mechanics, I develop a model of the stacking structure (in the form of an epsilon-machine) that makes complete use of all the information contained in the diffraction spectra (both Bragg-like and diffuse scattering). This framework allows for the calculation of average stacking energies and configurational entropies. I contrast this approach with previous descriptions of planar disorder and show that it offers a much more general framework for characterizing all levels of disorder, while traditional methods tend only to capture small deviations from crystallinity. Further, the graphical description for stacking structure that our model produces provides not only a quantitative measure of the amount of disorder but also an intuitive way to categorize different types of disorder. I illustrate this technique on several zinc sulphide diffraction spectra.

Last updated: 26 April 2009. Copyright © 2008-2010 by Dowman P. Varn. Contact: dpv@ComplexMatter.org

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