Diffuse scattering occurs from all crystalline materials at all temperatures and arises from disorder, leading to the temporary or permanent breakdown of space group symmetry. It contains information on the deviation from the average structure, so an understanding of the diffuse scattering is crucial to a full understanding of the overall structure of the material. Diffuse scattering can occur anywhere in the diffraction pattern, including beneath and between Bragg peaks. Because diffuse scattering can arise from a number of sources, the analysis can be extremely complex in even the simplest of materials.

The use of a large area detector with a wide dynamic range, such as the RAPID II imaging plate system, allows for an efficient survey of reciprocal space. The crystal can be oriented to allow specific slices of data (e.g. hk0, h0l, and 0kl) to be collected. These are the usual starting places for diffuse scattering modeling calculations.

Pentachloronitrobenzene (PCNB) exhibits six-fold orientational disorder in the solid-state, which gives rise to structured diffuse scattering both around and between Bragg peaks that remains as a function of temperature. In earlier studies of PCNB, synchrotron radiation was needed to observe the weak effects of diffuse scattering, but the instability of the incident beam made scaling difficult.

Using the RAPID II, diffuse scattering patterns are clear with 10-minute exposures. The images shown below are aligned close to the hk0 slice. The left pattern comes from the RAPID II and the right is reconstructed from synchrotron data. Even the weak diffuse features seen in the synchrotron image are clearly visible in the RAPID II image.

Results courtesy of Andy Parkin, Lynne H Thomas and Chick C Wilson, Structural Chemistry Group,  University of Glasgow