X‐ray diffraction study of the structural change from 2 H to 4 H in CdI 2 crystals

The structural changes, 2 H → faulted 2 H → faulted 4 H → 4 H , in CdI 2 crystals, which are caused by successive heat treatments, were studied by X‐ray diffraction. The faulted 2 H and faulted 4 H structures, which give diffraction patterns composed of sharp spots and diffuse streaks, were solved on the assumption that sharp spots arise from the `average structure' and diffuse streaks from a stacking disorder of layers. It was revealed that (1) each of the faulted 2 H and faulted 4 H structures is maintained unchanged over a certain range of heating temperature and (2) when two kinds of layer, V and V ′, are stacked in the faulted structures, a small number of V ′ layers are always followed by a large number of V layers.