Pair Distribution Function

Whereas Bragg analysis provides a description of the average structure of a material, total scattering provides a view of the local structure. It should be noted that this is still a bulk analytical technique, i.e. scattering occurs from the entire sample, but that it provides an alternative viewpoint of the structure.

Both X-ray and neutron total scattering experiments are possible, and are highly comple mentary. The need for data measured over a broad Q-range, necessitates the use of spallation neutrons or high-energy X-rays, for which there are optimised instruments available e.g. Polaris and I15/XPDF. As is apparent from Eq. 2.18 and Eq. 2.19, the PDF and F(Q) are different representations of the same information (both contain the local structural information lacking in the Bragg peaks alone). Whilst other local structural probes exist, such as EXAFS and NMRspectroscopy, they may be limited (depending on the system under investigation) as they provide information for only the first couple of shells, whilst the PDF is capable to describing much longer correlations.