Mode (3): Debye-Scherrer

Mode (3): Debye-Scherrer

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Mode (3): Debye-Scherrer

The term Debye-Scherrer is named after the originators, Debye, Scherrer and Hull, and is one of the oldest known powder diffraction geometries, though originally it was used only with photographic film on a "powder diffraction camera". It uses a near-parallel incident beam of X-rays with sufficient cross-section to bathe the whole powder-sample. One of its virtues is its simplicity as illustrated by the following schematic of the Debye-Scherrer camera/diffractometer.

Diffractometer

Camera

If we translate this geometry into the context of a synchrotron powder diffractometer we get the arrangement depicted in the schematic below. The sample is usually held in a glass capillary, which spins on its axis to increase the number of crystallite orientations offered to the incident X-ray beam, and of course the photographic film is replaced by a detector which scans around the full 2θ range by rotating around the capillary; also shown is an example of a pattern collected this way from Aerinite, a completely new mineral type discovered in Morocco in 1997.

The main advantages of this method are that

it is relatively easy to use;
it produces a very good diffraction peak shape (the significance of peak shape will become more apparent later during the course).

There are no real disadvantages to this method, though it is not practical to use it for high pressure work. Also some purists do not like to have scattering in their pattern from the glass nor have the inconvenience of loading their samples into a narrow capillary.

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Author(s): Paul Barnes
Simon Jacques
Martin Vickers