Polytypism and Related Phenomena in CdBr₂-Doped Dendritic Single Crystals of Cadmium Iodide

Abstract

Dendritic single crystals of CdI 2 , doped with 3% CdBr 2 , were grown from vapour phase in vacuum. The crystals exhibited well developed dendritic morphology. They were characterized by X-ray diffraction for their polytypism and related phenomena of streaking and arcing. The CdI 2 common polytype 4H was found to occur exclusively in 28% of cases and in combination with the poylytype 12R in the rest of the cases. The frequency of occurrence of streaking and arcing were found to be rather high, viz 47 and 25%, respectively. The results point to a large-scale formation of dislocations and the consequent stacking faults inside the crystals, presumably created due to stresses produced in the host structure by the introduction of doped ions. Optical and scanning electron-microscopic study of the surface features shows a well developed dendritic morphology conforming with the hexagonal symmetry of the crystals.