X-Ray and Neutron Diffraction Techniques

Abstract

X-ray diffraction techniques have greatly contributed to our knowledge of the cell geometry and atomic structure of feldspars. Structure analysis using the intensity of the Bragg diffractions yields the electron distribution in the average unit cell as described in Part 1. Single-crystal techniques are particularly valuable for characterizing the geometry and symmetry of the unit cell and for determining the nature of and the angular relations between the components of feldspar intergrowths. Powder X-ray diffraction techniques lose the three-dimensional information inherent in single-crystal techniques and have insufficient sensitivity to permit detection of subsidiary diffractions. They provide a much less complete characterization of phases and complex intergrowths, compensated in part by their greater spead and precision. X-ray methods are not suitable for the determination of the textures of complex phases and intergrowths as they do not allow imaging in direct space. Elec- tron-optical methods are now mandatory for textural studies of very fine intergrowths and modulated structures, as they allow the direct comparison of the diffraction pattern and the electron image of extremely small areas (Chap. 10). Neutron-diffraction techniques are too costly for routine work, but are very valuable for determining atomic coordinates, site distributions and the dynamics of phase transitions (Part 1).