Powder Diffraction

Example of a powder diffraction pattern.

Example of a powder diffraction pattern.

 

As it is not always possible to grow single crystal adequate for diffraction, powder diffraction can be measured on the bulk sample. As a powder sample consists of a multitude of single crystals of (hopefully) the same crystal form, which are randomly oriented, the powder diffractogram consists of the overlay of an infinite number of single crystal diffractograms with random orientation. Thus, a powder diffractogram, represented in two dimensions, contains rings concentric to the incident beam. The usual final diffractogram is a radial cut through those rings resulting in a plot of the measured intensity vs. the diffraction angle.

Lately, the diffraction angle has been exchanged with the momentum transfer Q, which is independent from the wavelength following

Q = (4 π sin(θ)) / λ

Using Q has advantages especially when using different radiation or radiation with tuneable wavelength.