Lattice dynamics of the Zn–Mg–Sc icosahedral quasicrystal and its Zn–Sc periodic 1/1 approximant

Abstract

Quasicrystals are long-range-ordered materials that lack translational invariance, so the study of their physical properties remains a challenging problem. Here, we have carried out inelastic-X-ray- and neutron-scattering experiments on single-grain samples of the Zn-Mg-Sc icosahedral quasicrystal and of the Zn-Sc periodic cubic 1/1 approximant, with the aim of studying the respective influence of the local order and of the long-range order (periodic or quasiperiodic) on lattice dynamics. Besides the overall similarities and the existence of a pseudo-gap in the transverse dispersion relation, marked differences are observed, the pseudo-gap being larger and better defined in the approximant than in the quasicrystal. This can be qualitatively explained using the concept of a pseudo-Brillouin-zone in the quasicrystal. These results are compared with simulations on atomic models and using oscillating pair potentials, and the simulations reproduce in detail the experimental results. This paves the way for a detailed understanding of the physics of quasicrystals.

Phononic filter effect of rattling phonons in the thermoelectric clathrate Ba8Ge40+xNiEuchner1, Pailhés2, Nguyen3 et al. 2012Phys. Rev. B909630View full textAdd to dashboardCite

“…As k increases, the spectral weight of the TA phonons is first transferred to the first guest phonon peak at E 1 and then to the second one at E 2 . Interestingly, similar effects have been observed in quasicrystals and large unit cell crystals [19,20]. The energy of the guest phonons at E 1 increases significantly during this process, shifting from 5.4 meV at the zone center to 6 meV at k=0.5 without any sizable change in its energy width (see Fig.…”

In-situ high-pressure X-ray diffraction on the Zn6Sc 1/1 periodic cubic approximant to a quasicrystal

“…1a. This is confirmed by molecular dynamics (MD) simulations with oscillating pair potentials that also reproduce the phonon spectra in this phase [4]. Moreover, using quasielastic neutron scattering [15] and atomic-scale MD simulations [15,16], it has been shown that the Zn tetrahedron behaves as a single 'molecule' that reorients dynamically above T c , conferring an unique 'dynamical flexibility' to the Zn 6 Sc.…”

“…Recent progress has been achieved in understanding their atomic structure [3] and physical properties [4] thanks to discoveries of a stable i-Cd 5:7 Yb [5] binary icosahedral phase and an isostructural i-Zn 80 Mg 5 Sc 15 phase [6]. In both systems, the quasicrystal and its periodic approximant can be synthesized with almost the same chemical composition [7,8].…”

Phonons, phasons and atomic dynamics in quasicrystals

“…27,28 This would require a detailed modeling, and the proper time scales to be set up, a work which can probably be carried out in the Tsai type icosahedral quasicrystal compounds where detailed knowledge of the atomic structure and adapted potentials are available. 29,30 …”