The theory of diffuse X-ray scattering and its application to the study of point defects and their clusters

The theory of the diffuse scattering by point defects and by defect clusters is reviewed. For a small concentration of statistically distributed point defects the symmetry of the long ranging part of the displacement field and the strength of the defects can be obtained from scattering measurements close to the reciprocal lattice points (Huang scattering). In addition to the (symmetrical) Huang scattering an asymmetry of the scattering is observed. For defects with sufficiently large displacements, the sign of this asymmetric scattering determines the sign of the displacement field around the defect and its magnitude yields information about the magnitude of the displacements close to the defect. For defect clusters the diffuse scattering is strongly modified. The Huang scattering very near to the Bragg reflection increases in direct proportion to the number of point defects in the cluster. For larger distances q from the Bragg reflection the intensity decreases as 1/q4.