Diffuse X-ray scattering from the displacement field of point defects and defect clusters

This review gives first a short introduction to the theoretical relations between experimentally observed diffuse scattering results and the desired information about defects. The situation is discussed under which diffuse scattered X-ray intensity from defects can be distinguished from other diffuse intensities (thermal diffuse scattering, Compton scattering). A typical experimental set-up is described to show what the requirements are in experimental resolution and how intensity distribution in reciprocal space can be measured most conveniently. A few typical experiments are discussed to demonstrate the physical potential of this method for studying impurities in metals and radiation-induced defects and defect clusters in ionic crystals. Special emphasis is given to the comparison of the experimental results with theoretical predictions; the intensity close to the Bragg peaks (Huang scattering) falls off as 1/_g², g being the distance from a reciprocal-lattice point G. The scattering intensity goes as G². The intensity distribution in reciprocal space gives typical isointensity curves from which the symmetry of the double force tensor and its components can be deduced. Together with the measured shift of a Bragg peak, measurement of absolute scattering intensity gives a unique way of determining the defect concentration. Further away from the Bragg peaks (asymptotic scattering) the intensity is proportional to 1/g⁴ and shows characteristic oscillations.