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 Mِssbauer spectroscopy (QMS) was used to probe the iron phason dynamics. Inelastic nuclear-resonant absorption (INA) of synchrotron radiation and inelastic neutron scattering (INS) were used to study the iron-partial as well as the neutron-weighted vibrational DOS, g(E). The lattice specific heat, Clatt(T), calculated from the neutron-weighted g(E) agrees with the experimental one in the low temperature range where an anomalous power law had previously been found. These results are discussed in terms of possible non-acoustic 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 phason jumps. These different properties are related to the specific local environments of Al, Cu and Fe in i-AlCuFe.