Crystals of potassium alum, pure and slightly doped with Cr³⁺, were grown from aqueous solution by slow temperature lowering. In addition, short re-dissolution periods were introduced in order to provoke growth defects and changes of growth rates. Crystal slices of about 1 mm thickness were studied by conventional LANG X-ray diffraction topography using MoK α radiation. For Cr-doped crystals, boundaries between {100}, {100}and {111} growth sectors appear by pronounced dynamical X-ray topographic contrast similar to that of stacking faults. Re-dissolution experiments provoke the formation of inclusions on {100} faces, followed by an increase of the {100} growth rate by the factor of about six, relative to the neighboured {111} faces. X-ray topographs show that this increase is correlated with the formation of dislocations, which interestingly have pure-edge character. During further growth these dislocations penetrate the {100}-{111} growth sector boundary and vanish from the {100} face, which slows down and finally adopts its former growth rate before re-dissolution.

Keywords: potassium alum, solution growth, growth-sector boundary, growth-rate dispersion, dislocations, X-ray topography

---

The full text of this paper in pdf-Format:

If you came directly to this page, click this symbol to go to the homepage of CRT.