Dynamics in the icosahedral quasicrystal i-Al62Cu25.5Fe12.5: phonons and phasons

This work concerns both the atomic-partial phonon (vibrational) density of states (VDOS), as well as phason-hopping at high temperatures. Quasielastic Mossbauer spectroscopy (QMS) was used to probe the iron phason dynamics. I nelastic nuclear-resonant absorption (INA) of synchrotron radiation and ine lastic neutron scattering (INS) were used to study the iron-partial as well as the neutron-weighted vibrational DOS, g(E). The lattice specific heat, C-latt(T), calculated from the neutron-weighted g(E) agrees with the experi mental one in the low temperature range where an anomalous power law had pr eviously been found. These results are discussed in terms of possible non-a coustic modes at low energy. We find from QMS studies that iron atoms jump two orders of magnitude slower than copper. The EFG shows a change in slope at ca. 825 K related to a transition from simple to more complicated phaso n jumps. These different properties are related to the specific local envir onments of Al, Cu and Fe in i-AlCuFe. (C) 2001 Elsevier Science B.V. All ri ghts reserved.