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. 2.5, p. 118

Section 2.5.1.2. Comparison between 2D-XRD and conventional XRD

B. B. Hea*

aBruker AXS Inc., 5465 E. Cheryl Parkway, Madison, WI 53711, USA
Correspondence e-mail: bob.he@bruker.com

2.5.1.2. Comparison between 2D-XRD and conventional XRD

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Fig. 2.5.1[link] is a schematic of X-ray diffraction from a powder (polycrystalline) sample. For simplicity, it shows only two diffraction cones; one represents forward diffraction [(2\theta\leq90^\circ)] and one represents backward diffraction [(2\theta\,\gt\,90^\circ)]. The diffraction measurement in a conventional diffractometer is confined within a plane, here referred to as the diffractometer plane. A point (0D) detector makes a 2θ scan along a detection circle. If a line (1D) detector is used in the diffractometer, it will be mounted on the detection circle. Since the variations in the diffraction pattern in the direction (Z) perpendicular to the diffractometer plane are not considered in a conventional diffractometer, the X-ray beam is normally extended in the Z direction (line focus). Since the diffraction data out of the diffractometer plane are not detected, the structures in the material that are represented by the missing diffraction data will either be ignored, or extra sample rotation and time are needed to complete the measurement.

[Figure 2.5.1]

Figure 2.5.1 | top | pdf |

Diffraction patterns in 3D space from a powder sample and the diffractometer plane.

With a 2D detector, the diffraction measurement is no longer limited to the diffractometer plane. Depending on the detector size, the distance to the sample and the detector position, the whole or a large portion of the diffraction rings can be measured simultaneously. Diffraction patterns out of the diffractometer plane have for a long time been recorded using Debye–Scherrer cameras, so the diffraction rings are referred to as Debye rings. However, when a Debye–Scherrer camera is used, only the position of the arches in the 2θ direction and their relative intensities are measured for powder-diffraction analysis. The diffraction rings collected with a large 2D detector extend further in the `vertical' direction and the intensity variation in the vertical direction is also used for data evaluation. Therefore, the terms `diffraction cone' and `diffraction ring' will be often be used in this chapter as alternatives to `Debye cone' and `Debye ring'.








































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