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Article Dans Une Revue International Union of Crystallography journal Année : 2016

Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

Résumé

The detailed atomic structure of the binary icosahedral (i) ScZn7.33 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-YbCd5.7 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-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 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 K-2/K-1 = -0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye-Waller factor, which explains the vanishing of 'high-Q(perp)' reflections.

Domaines

Matériaux

Dates et versions

hal-01384366 , version 1 (19-10-2016)

Identifiants

Citer

Tsunetomo Yamada, Hiroyuki Takakura, Holger Euchner, Cesar Pay Gómez, Alexei Bosak, et al.. Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal. International Union of Crystallography journal, 2016, 3 (4), pp.247 - 258. ⟨10.1107/s2052252516007041⟩. ⟨hal-01384366⟩
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