On the diffraction features of two‐layer systems. Application to Ni_3±xTe₂

The ordering process of some two‐layer systems such as Ni_3±xTe₂ is characterised by the appearance of a small number of quasi‐incommensurable superlattice reflections, of which the positions shift continuously with composition. Although for each system, a structural model can be derived by trial and error procedures, it is the purpose of this work to explain such characteristic diffraction features more systematically in terms of a shear‐structure like model. The results are applied to confirm the previously derived structures for the ordered phases in Ni_3±xTe₂.