Errors in quantitative analysis of diffuse scattering from alloys

Errors in separating diffuse scattering resulting from local order from that from static and dynamic displacements have been examined; the Borie-Sparks symmetry procedure was employed, which includes second-order terms in the displacements. The largest source of error when X-rays are employed is the variation in the ratio of scattering factors across the volume measured in reciprocal space. Large errors in the Warren local-order parameters result for clustering systems with displacement terms of the same order as the local-order parameters (or larger), but not if the size terms are smaller. For systems with local order the errors in these parameters are small. Uncertainties in the size terms are always appreciable. Other errors that were considered are: higher-order terms, extrapolation under Bragg peaks, errors in Compton scattering, background and surface roughness, and uncertainties in composition or polarization resulting from a monochromator.