Effect of growth conditions on polytypism in cadmium iodide crystals

Abstract

The effect of temperature, rate of crystallization and impurities on polytypism in cadmium iodide crystals has been studied by X-ray diffraction in nearly two and a half thousand polytypes. The frequency of occurrence of the small period polytypes 2 H and 6 H decreases as the temperature of growth increases, thus implying that these polytypes may be regarded as low temperature modifications of cadmium iodide. A slower rate of crystallization promotes the growth of the common polytype 4 H. The frequency of occurrence of the unidentified polytypes rises with increase in both the temperature and the rate of crystallization. The presence of dust particles promotes the incidence of polytypism as well as the growth of the total number of crystals in a particular batch. The results have helped to explain the mutually contradictory empirical conclusions of the earlier investigations.