High‐resolution electron microscopic and electron diffraction study of non‐stoichiometric phases in Cu_3—xTe₂

The electron diffraction patterns of Cu_3—xTe₂ are characterized by the occurrence of “incommensurate” superlattice reflections of which the positions with respect to the “basic” reflection, shift in a systematic manner with composition and/or degree of order. Similar effects were described previously with reference to Ni_3±xTe₂. Such diffraction patterns are interpreted in terms of “shear structures” derived from a simple hypothetical reference phase, for which a structure could be proposed. The incommensurability results from the occurrence of a mixture of spacings between shear planes. The model is consistent with high‐resolution images. Optical diffraction experiments from two‐dimensional gratings representing the structure also support the models.