• Yamada, Tsunetomo

Abstract

<jats:p>The detailed atomic structure of the binary icosahedral (i) ScZn<jats:sub>7.33</jats:sub>quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd<jats:sub>5.7</jats:sub>one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn<jats:sub>7.33</jats:sub>and i-YbCd<jats:sub>5.7</jats:sub>was found to lie in the icosahedron shell and the DFP where in i-ScZn<jats:sub>7.33</jats:sub>chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants<jats:italic>K</jats:italic><jats:sub>2</jats:sub>/<jats:italic>K</jats:italic><jats:sub>1</jats:sub>= −0.53,<jats:italic>i.e.</jats:italic>close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of `high-<jats:italic>Q</jats:italic><jats:sub>perp</jats:sub>' reflections.</jats:p>

Topics

• impedance spectroscopy
• cluster
• x-ray diffraction
• anisotropic
• chemical composition