The Cdl2 and related structures

Portions of two layers of the Cdl2 structure. The small circles represent metal atoms. 

Cdl2 itself, mixed crystals CdBrl, Pbl2, etc. crystallize with more than one of these structures and also with structures with much more complex layer sequences more than 80 polytypes of Cdl2 have been characterized. These are not of special interest here since their formation is obviously connected with the growth mechanism and they are all built of the same basic layer. We wish to show here how this very simple layer is utilized in the structures of a variety of compounds, and we shall not be particularly concerned with the mode of stacking of the layers. We shall describe five types of structure, starting with those in which the layer is of the simplest possible type, namely, in compounds MX2 or M2X in which all M atoms or all X atoms are of the same kind. 

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