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
Abstract:
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.