On Growth and Structure of Vapor‐Grown Cadmium Iodide Crystals

Abstract

Cadmium iodide crystals have been grown by the vapor phase technique. Under different thermal and supersaturation conditions, cadmium iodide crystals of the same morphological form and shape, but of different size and thickness, have been obtained. No spirals are observed on the crystals which grow with their basal planes normal to the wall of the growth tube, whereas, spirals have been observed on crystals grown on a glass substrate at high super‐saturation. The observations indicate that a screw dislocation mechanism is not operative in the growth of crystals in the present case. The growth starts with a dendritic skeleton and then changes to flat platelets by the filling in process and by two dimensional nucleation. Formation of spirals on crystals grown on glass slides has been attributed to adsorbed impurities or debris and irregularities on the substrate surface. An x‐ray study of the crystals has revealed that nearly all vapor‐grown crystals show the most stable basic polytype (4H) of . Observations indicate that conditions of growth play an important role in deciding the structure.