Regensburg 2002 – wissenschaftliches Programm
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M: Metallphysik
M 11: Quasikristalle IV
M 11.4: Fachvortrag
Dienstag, 12. März 2002, 17:15–17:30, H6
The Iron Local Dynamics in i-AlCuFe Quasicrystals: Quasielastic Scattering — •R.A. Brand1, J. Voss1, B. Frick2, and Y. Calvayrac3 — 1Institute of Physics, University of Duisburg, Germany — 2ILL,Grenoble, France — 3C.E.C.M./C.N.R.S., 15 rue G. Urbain, Vitry, France
Phason defects are important for the understanding of both the structure and atomic motion in quasicrystals. These defects can lead to short-ranged atomic motion not involving vacancies and may lead to a new diffusion mechanism. We have studied icosahedral i-Al62Cu25.557Fe12.5 using quasielastic Mössbauer spectroscopy (QMS) and quasielastic neutron scattering (QNS) for T ≤ 1100 K. For QMS we find that the Lamb-Mössbauer factor f(T) of the central elastic (quadrupole-split) line decreases abruptly below the Debye result fD(T) for T > 580 K where an additional quasielastic signal appears. This is due to local “cage motion” of iron atoms due to phason jumps. The quasielastic line width Γ(T) shows that iron atoms jump on a time scale of approximately (ℏ/2.3µeV) at T = 1000 K, about two orders of magnitude smaller than that found for copper. The electric field gradient shows a break in slope at ca. 825 K, related to a transition from simple (isolated iron) to more complicated (co-operative) phason jumps. For QNS, we show that the quasielastic signal, present for samples with natural iron (σ = ), practically disappears for samples with 57Fe (σ = ), proving that iron is involved in this jump process. Unfortunately, the range of q (at IN16 of ILL) was not large enough to determine the average jump distance.