Modulated-Crystal Model for the Twelvefold Quasicrystal Ta₆₂Te₃₈

A transmission electron microscopy study reveals that the so-called twelvefold quasicrystal Ta₆₂Te₃₈ is a crystal subjected to structure modulation. It is composed of two incommensurate layers rotated by 30° to each other about their normal. High-resolution electron microscope images show the formation of commensurate domains and their discommensuration. The observed electron diffraction patterns may be explained by a kinematical calculation for the commensurate cell, designated as a 7 × 7 cell. The modulation is considered to be due to the rearrangement of atomic vacancies in response to the occurrence of charge-density waves.