Electron microscopy analysis of decagonal quasicrystals in the Al–Cu–Co–Si system

Abstract

Abstract Large needle-shaped grains of a decagonal quasicrystal in the Al–Cu–Co–Si quaternary system were prepared by slow cooling from the melt. Scanning electron microscopy, X-ray diffraction and convergent-beam electron diffraction patterns confirmed that the needles have a decagonal quasicrystal structure. Thin slices normal to the tenfold directions were prepared for transmission electron microscopy. Diffuse streaks along symmetric directions around the fundamental spots and in between weaker diffraction spots as well as satellite spots were observed in the tenfold diffraction patterns. Bright-field and dark-field images showed discontinuous lines or striations lying perpendicular to the direction of diffuse streaking. Dark contrast at the point of discontinuity of the fringes are observed along a particular direction. High-resolution electron microscopy images also indicated features corresponding to the striation contrast. The striation contrast is shown to be associated with a phason disorder boun...