Inelastic-neutron-scattering measurements of phonons in icosahedral Al-Li-Cu

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Abstract
Inelastic-neutron-scattering measurements on a single grain of icosahedral Al-Li-Cu are presented. Within experimental error the acoustic-phonon dispersion at small, but finite, q is independent of direction, confirming the isotropic elasticity expected for icosahedral crystals. By following the longitudinal-phonon dispersion curve along a fivefold axis we can identify the location of ‘‘quasi-Brillouin-zone boundary.’’ The measurements also suggest the presence of an optical or localized mode along the twofold axis at approximately 10–11 meV. We compare these results to theoretical calculations for one- and two-dimensional quasiperiodic systems.