Pair Distribution Function
The pair distribution function (PDF) corresponds to a histogram of interatomic distances. Any atom of the sample serves as an arbitrary centre, from which all interatomic distances to all other atoms are measured. All interatomic distances are summed up and projected over the radius r.
The figure shows the ab-plane of the wurtzitic crystal structure of zinc oxide (ZnO) with blue Zn and red O atoms. The summation of the interatomic distances is exemplarily shown for a blue Zn atom serving as centre atom. Consequently as in a histogram, each peak corresponds to a distance, where neighbouring atoms are most likely found in the sample.
The PDF is gained from X-ray or neutron scattering data, occasionally from electron diffraction. We have a lab PDF diffractometer in our workgroup. Additionally, high-quality PDF data is collected at large scale research facilities, most frequently using high-energy X-rays (50 – 70 keV) in order to measure the scattering data to very large diffraction angles.