International
Tables for
Crystallography
Volume H
Powder diffraction
Edited by C. J. Gilmore, J. A. Kaduk and H. Schenk

International Tables for Crystallography (2018). Vol. H, ch. 2.1, pp. 31-32

Section 2.1.4.3. Range of applications

A. Kerna*

aBruker AXS, Östliche Rheinbrückenstrasse 49, Karlsruhe 76187, Germany
Correspondence e-mail: arnt.kern@bruker-axs.de

2.1.4.3. Range of applications

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It is the flexibility of today's X-ray diffractometers that leads to their usefulness for a wide range of X-ray scattering techniques beyond traditional X-ray powder `Bragg diffraction'. Table 2.1.2[link] provides an overview.

Table 2.1.2| top | pdf |
X-ray applications for with modern X-ray diffractometers

X-ray scattering
  Powder diffraction
    Qualitative (phase identification) and quantitative phase analysis
    Indexing, structure determination and structure refinement from powder data
    Microstructure analysis (texture, size, strain, microstrain, disorder and other defects)
    Pair distribution function analysis (`total scattering')
  Thin-film analysis
    Grazing incidence X-ray diffraction (GIXRD)
    X-ray reflectometry
    Stress and texture
    High-resolution X-ray diffraction
    Reciprocal-space mapping
    In-plane GIXRD
  Single-crystal diffraction
    Chemical crystallography
    Protein crystallography
  Small-angle X-ray scattering
  X-ray topography
 
X-ray absorption
  X-ray radiography (X-ray-absorption-based imaging)
 
X-ray emission
  X-ray fluorescence

X-ray scattering techniques represent the vast majority of techniques that X-ray diffractometers are used for. Properly configured, however, the same instrument can also be used to collect X-ray absorption (X-ray radiography) or X-ray emission (X-ray fluorescence) data, even if the achievable data quality cannot compete with dedicated instruments.

For X-ray radiography, an instrument will be configured in transmission geometry with the X-rays projected towards a specimen. X-rays that pass through the specimen can be detected to give a two-dimensional representation of the absorption contrast within the specimen. For tomography, the X-ray source and detector will be moved to blur out structures not in the focal plane. Multiple images can be used to generate a three-dimensional representation of the specimen by means of computed tomography. Obvious disadvantages are the large effective focal spot size of the X-ray sources and the relatively low resolution of the detectors that are typically used for powder diffraction, which, in combination with a limited adjustability of both the X-ray-source-to-specimen and specimen-to-detector distances, lead to substantial unsharpness issues and poor resolution. High-quality images can be achieved when using micro-focus X-ray sources and charge-coupled device (CCD) detectors with focus and pixel sizes smaller than 10 µm, respectively, but such an instrument configuration is not suitable for applications requiring ideal powders (see also Sections 2.1.6[link] and 2.1.7).

Collecting X-ray fluorescence data is comparatively straightforward. Data can be collected simultaneously to X-ray scattering data when employing a suitable detector, such as an energy-dispersive detector (Section 2.1.7.2.3[link]). There are a couple of disadvantages to be considered, such as absorption issues (the specimen will be normally measured in air rather than in vacuum, hampering the analysis of light elements) and the inefficiency of excitation by the characteristic line energies of the X-ray source anode materials typically used for diffraction (hampering the analysis of elements with higher atomic numbers than that of the anode material).








































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