Dynamics in the icosahedral quasicrystal i-Al 62Cu 25.5Fe 12.5: phonons and phasons

Abstract

This work concerns both the atomic-partial phonon (vibrational) density of states (VDOS), as well as phason-hopping at high temperatures. Quasielastic Mössbauer 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, C latt( 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.