X-ray diffuse scattering

The routine use of area detectors such as CCD’s for service crystallography, and the continued improvement in detector sensitivity and the intensity of lab-based X-ray sources, means that diffuse scattering is seen on a regular basis. Often, the detection of diffuse scattering during crystal screening leads to rejection of the crystal. However, the correct interpretation of diffuse scattering patterns, even on a qualitative basis, can help in structure solution and in the development of an appropriate model of disorder for the structure refinement. In this presentation we will review the common types of diffuse scattering that are observed in molecular compounds, ceramics and minerals, and demonstrate some software tools for their characterization. Single-crystal diffraction measurements under either varying temperature or pressure can provide further insights in to the structural cause of diffuse scattering. Changes with pressure or temperature in the intensity or pattern of diffuse scattering imply that the structural origin of the disorder is displacive or dynamic in nature (as in nepheline and some relaxor ferroelectric perovskites), whereas the persistence of the diffuse scattering points to an origin in atomic ordering (as in FeO).