POLYTYPISM AND RELATED PHENOMENA IN CDBR2-DOPED DENDRITIC SINGLE-CRYSTALS OF CADMIUM IODIDE

Dendritic single crystals of CdI2, doped with 3% CdBr2, were grown fro m vapour phase in vacuum. The crystals exhibited well developed dendri tic morphology. They were characterized by X-ray diffraction for their polytypism and related phenomena of streaking and arcing. The CdI2 co mmon 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 freq uency of occurrence of streaking and arcing were found to be rather hi gh, viz 47 and 25%, respectively. The results point to a large-scale f ormation of dislocations and the consequent stacking faults inside the crystals, presumably created due to stresses produced in the host str ucture by the introduction of doped ions. Optical and scanning electro n-microscopic study of the surface features shows a well developed den dritic morphology conforming with the hexagonal symmetry of the crysta ls.