Diffractometry and reflection profiles of anisotropic mosaic and split crystals

Both anisotropic mosaicity and splitting of a crystal is described by means of a 'rotational cluster' model with a predominant rotation about a vector A. Procedures are outlined to obtain A from intensity scans made at different orientations about the diffraction vector, and to compute for all reflections those diffractometer setting angles for which the effect from anisotropy or splitting upon the profile is minimal. The relevant Fortran programs, ANIVEC and ANIMO, for our Enraf-Nonius CAD4F four-circle diffractometer system are available.