It has been formally announced that the proposal for the development of a dedicated beamline instrument at the Diamond synchrotron source for the measurement of pair distribution functions (PDF), XPDF, should now move to the design and construction phase. Our group has played a significant part in the development of the proposal for XPDF, and will be involved in it's development. This instrument, which will complement PDF instruments at the ISIS neutron scattering facility, will play an important part in our future research.
The PDF is effectively a histogram of instantaneous interatomic distances in a material. For highly disordered materials it provides the only experimentally-determined information about the atomic structure. For many crystals, the structure on a local scale may be significant affected by local fluctuations so that the PDF is rather different from what might be expected from the crystal structure. These fluctuations can give rise to important properties, and thus is an essential part of understanding the structure of materials.