The Benefits of Rotating Sample Holders for X-ray Diffraction on Textured or Grainy Samples
The perfect powder sample for X-ray diffraction is a homogeneous powder made up of a large number of perfectly spherical particles, with narrow crystallite size distribution, that are randomly oriented in the sample holder. In reality, samples very rarely align exactly with these requirements, and steps must be taken to overcome the issues caused by inhomogeneous or oriented samples.
Introduction
Not all polycrystalline materials consist of a quasi-infinite number of randomly distributed crystallites of homogeneous size. In reality, most samples show a certain degree of inhomogeneity in crystallite size and shape throughout the sample. As long as these inhomogeneities are small, they typically do not affect the diffraction experiment. However, in some materials, the inhomogeneities are significant and can lead to errors in the diffraction pattern. These effects can be either texture, also called preferred orientation, or graininess. Powder materials with texture may comprise oddly shaped particles or crystallites that orient themselves in a certain direction in the sample. Only the lattice planes whose normal n is parallel to the scattering vector q are contributing the XRD pattern. This means in oriented samples certain lattice planes contribute more strongly to the diffractogram than others, leading to differences in peak intensities, i.e., the intensities differ from what would be expected for a “perfect” powder.
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