Direct structure imaging of long period Ni_3±xTe₂ superstructures

High‐resolution electron microscopy is used to study by “in situ” heating, the dynamical formation of superstructures in the Ni_3±xTe₂ system. The structures so obtained are intermediate with respect to the degree of order between the low‐temperature monoclinic phase and the high‐temperature tetragonal phase. During this transformation, a wide variety of gradually changing superstructures is observed, characterized in the diffraction pattern by the presence of quasi incommensurate shifting reflections. The stacking sequences, as deduced from the observed structure images, using an empirically derived imaging code, are in agreement with the previously proposed structure model, in which phases are considered as being built from two kinds of layers in the octahedral interstices of a deformed cubic close packed arrangement of tellurium atoms: planes filled predominantly with Ni atoms and planes filled predominantly with vacancies.