This chapter provides a complete account of the method of structure refinement of incommensurately modulated structures and incommensurate composite crystals. Modulation functions for displacive modulation, for occupational modulation, and for modulation of anisotropic displacement parameters (ADPs; temperature parameters) are described by truncated Fourier series, thus providing the Fourier amplitudes as parameters of the structure model. Constraints and restraints on the structural parameters are discussed, including the use of rigid bodies and non-crystallographic site symmetries. The block-wave (crenel) function and the saw-tooth function are presented as special modulation functions that may be alternatives to Fourier series. Next to structure refinements against single-crystal diffraction data, refinements of incommensurate structures against powder diffraction data (Rietveld refinement) are presented.
Oxford Scholarship Online requires a subscription or purchase to access the full text of books within the service. Public users can however freely search the site and view the abstracts and keywords for each book and chapter.
If you think you should have access to this title, please contact your librarian.