Inelastic neutron scattering (INS) is a powerful tool for studying the atomic dynamics of disordered systems, providing information about vibrational modes and their contribution to thermodynamic properties. In this paper, we present a comparative study of the atomic dynamics of icosahedral Al62Cu25.5Fe12.5 and tetragonal Al70Cu20Fe10 obtained by the INS method.
The NVR experiments were carried out on the IN4 spectrometer at the Institut Laue-Langevin (ILL), Grenoble. The samples were prepared by arc melting followed by heat treatment to obtain a single-phase structure. The obtained NVR spectra were analyzed using the generalized vibrational density function (VDFS) model.
Using inelastic cold neutron scattering, we measured the global dynamic structure factor S(Q, ω) and the generalized vibrational density of states G(ω) for icosahedral Al62Cu25.5Fe12.5 and, as a reference, for tetragonal Al70Cu20Fe10. In contrast to theoretical predictions expecting pronounced spectral features for the icosahedral phase, we did not observe them despite using a sample with the highest achieved concentration of icosahedral AlCuFe. Instead, a broad intensity distribution in S(Q, ω) and a smeared two-peak structure in G(ω) reminiscent of amorphous solids were found for the icosahedral alloy. In contrast, the dynamic structure factor and phonon density of states of tetragonal AlCuFe, measured under the same conditions, show distinct features over the entire energy range studied.
The results show significant differences in the FPS for the icosahedral and tetragonal phases. The icosahedral phase exhibits a broader distribution of vibrational modes, indicating a higher degree of disorder. The tetragonal phase exhibits sharper peaks, indicating a more ordered structure. Debye temperature analysis showed that the icosahedral phase has a lower Debye temperature than the tetragonal phase, indicating a “softer” atomic structure.
Author: T Klein, G Pares, J.-B Suck, G Fourcaudot, F Cyrot-Lackmann
Institute: Laboratory of Electronic Properties of Solids, CNRS, BP 166, F-38042 Grenoble, France, Institut Laue-Langevin, P.O. Box 156, F-38042 Grenoble, France