International Tables for Crystallography

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X-ray diffraction from non-crystalline materials: the Debye model
S. Bates. International Tables for Crystallography (2019). Vol. H, ch. 5.6, pp. 617-648  [ doi:10.1107/97809553602060000971 ]

Abstract

This chapter introduces and explores a Debye diffraction approach to modelling X-ray diffraction data measured on non-crystalline materials from the perspective of materials characterization. Ideal non-crystalline materials are defined to be high-density liquid or solid molecular systems that can be considered to be essentially isotropic and random with no long-range inter-molecular order. X-ray diffraction measurements performed on these isotropic and random materials give essentially continuous diffraction patterns characterized by a series of diffuse halos and a lack of any discrete diffraction peaks. The measurement and analysis of continuous diffraction patterns is an application of total diffraction and requires specific data-processing techniques to transform the as-measured data into a suitable instrument-free form for Debye modelling. A data-processing methodology is discussed that allows the use of traditional laboratory-based X-ray diffractometers for the total-diffraction analysis. A simplified approach to Debye diffraction modelling of non-crystalline systems is introduced that makes use of single-molecule models along with an intermolecular packing function. The methodology is straightforward to employ for real-world materials characterization problems. For characterization of mixed non-crystalline systems, a quantitative chemometric method is presented that makes use of the continuous nature of non-crystalline diffraction patterns.


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About International Tables for Crystallography

International Tables for Crystallography is the definitive resource and reference work for crystallography. The multi-volume series comprises articles and tables of data relevant to crystallographic research and to applications of crystallographic methods in all sciences concerned with the structure and properties of materials.