title: Tetrahedron dynamics in the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and the cubic 1/1-approximant Zn6Sc.
abstract: A comparison of periodic approximants and their quasicrystalline counterparts offers the opportunity to better understand the structure, physical properties and stabilizing mechanisms of these complex phases. We present a combined experimental and molecular dynamics study of the lattice dynamics of the icosahedral quasicrystals i-ZnMgSc and i-ZnAgSc and compare it to recently published results obtained for the cubic 1/1-approximant Zn(6)Sc. Both phases, quasicrystal and approximant, are built up from large atomic clusters which contain a tetrahedral shell at the cluster centre and are packed either quasiperiodically or on a bcc lattice. Using quasielastic neutron scattering and atomic scale simulations, we show that in the quasicrystal the tetrahedra display a dynamics similar to that observed in the 1/1-approximant: the tetrahedra behave as a 'single molecule' and reorient dynamically on a timescale of the order of a few ps. The tetrahedra reorientation is accompanied by a large distortion of the surrounding cluster shells which provide a unique dynamical flexibility to the quasicrystal. However, whereas in the 1/1-approximant the tetrahedron reorientation is observed down to T(c) = 160 K, where a phase transition takes place, in the quasicrystal the tetrahedron dynamics is gradually freezing from 550 to 300 K, similarly to a glassy system.
authors: Institut für Theoretische und Angwandte Physik, Universität Stuttgart, D-70550 Stuttgart, Germany. euchner@itap.physik.uni-stuttgart.de
authors: H
authors: H
authors: Euchner
authors: T
authors: T
authors: Yamada
authors: S
authors: S
authors: Rols
authors: T
authors: T
authors: Ishimasa
authors: Y
authors: Y
authors: Kaneko
authors: J
authors: J
authors: Ollivier
authors: H
authors: H
authors: Schober
authors: M
authors: M
authors: Mihalkovic
authors: M
authors: M
authors: de Boissieu