Nanostructure investigation of the layered ternary compound Ni3–xSn1–yTe2

The structure of Ni3-xSn1-yTe2 is characterized by layered structural motifs related to an average NiAs/Ni2In-type. Order/disorder phenomena were analyzed via a detailed nanostructure investigation including electron diffraction and high resolution transmission electron microscopy (HRTEM) in conjunction with image simulation. Dependent on the stoichiometry, commensurate and incommensurate satellite reflections with respect to the parent NiAs structure were observed in Fourier transform and electron diffraction pattern as a result of occupational modulation of Te and Sn atoms. For the commensurate case a triplication of the c-lattice parameter is evident as a result of Sn-Te-Te stacking. Further, HRTEM micrographs indicate additional ordering phenomena along the c* direction depending on Ni/vacancy ordering which was rationalized by an alternating filling of van der Waals gaps with Ni. Also morphological defects in bright field images were observed. HRTEM investigations prove that these morphological defects are of structural nature, i.e. they are based on domains shifted relative to each other (antiphase boundaries)