7.2: X-Ray Diffraction Techniques

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Two types of targets are used in Bragg diffraction experiments: single crystals and powder targets.

Single Crystal

In a single crystal setup, an X-ray detector is mounted as shown in figure 7.2. A mechanical device keeps the detector oriented so that the angle of incidence equals the angle of reflection for the desired crystal plane. Peaks in the X-ray detection rate are sought as the angle \(\theta\) is varied.

The advantage of this type of apparatus is that diffraction peaks from only the selected crystal plane are observed.

Powder Target

The powder in a powder target is really a conglomeration of many tiny crystals randomly oriented. Thus, for each possible Bragg diffraction angle there are crystals oriented correctly for Bragg diffraction to take place. The detector is usually a photographic plate or an equivalent electronic device as illustrated in figure 7.3. For each Bragg diffraction angle one sees a ring on the plate concentric with the axis of the incident X-ray beam.

The advantage of this type of system is that no knowledge is needed of the crystal plane orientations. Furthermore, a single large crystal is not required. However, all possible Bragg scattering angles are seen at once, which can lead to confusion in the interpretation of the results.