Polytypism has been observed in a large number of materials where the nearest neighbor relationship between identical two-dimensional layers of atoms can be satisfied in more than one way. Cadmium iodide structure is a simple I-Cd-I layered structure with [CdI6]4- octahedron being the basic building block. Due to presence of overstoichiometric cadmium atoms during crystal growth and impurities in the starting material, the layers can be stacked in many ways. Taking into account some known structures of CdI2, work done on the overstoichiometric Cd atoms and purification of cadmium iodide it is noted that the presence of impurities in the starting material and excess cadmium atoms distorts the [CdI6]4- octahedron, which in turn give rise to formation of polytypes.
