The contrast factors of dislocations in cubic crystals: the dislocation model of strain anisotropy in practice

It has been shown recently that in many cases strain anisotropy in powder d iffraction can be well accounted for by the dislocation model of the mean s quare strain. The practical application assumes knowledge of the individual contrast factors C of dislocations related to particular Burgers, line and diffraction vectors or to the average contrast factors (C) over bar. A sim ple procedure for the experimental determination of (C) over bar has been w orked out, enabling the determination of the character of the dislocations in terms of a simple parameter q. The values of the individual C factors we re determined numerically for a wide range of elastic constants for cubic c rystals. The (C) over bar factors and q parameters were parametrized by sim ple analytical functions, which can be used in a straightforward manner in numerical analyses, as e.g. in Rietveld structure refinement procedures.