Papers by Keyword: Phasons

Abstract: The use of mechanical spectroscopy to characterize the quasicrystalline state of solid matter is reviewed. After a general, chronological survey of existing mechanical spectroscopy studies, which include elastic properties as well as various relaxation phenomena between lowtemperature tunneling processes and high-temperature background damping, three subjects are considered in more detail: (i) the nature of intrinsic relaxation phenomena, including relaxation peaks in Al-Pd-Mn single quasicrystals, (ii) hydrogen-induced loss peaks in Zr/Ti-based quasicrystals and their use as a probe, and (iii) the study of nano-quasicrystalline structures and amorphousquasicrystalline transitions. It is shown that by combined studies of different elastic and anelastic phenomena, mechanical spectroscopy can be a valuable tool to obtain information about the nature and motion of defects, about the type of local atomic order, and about phase transformations and different processes leading to the formation of quasicrystalline order.

Abstract: Mechanical loss (internal friction) measurements were applied to polycrystalline d- AlNiCo quasicrystals for compositions ranging from Al72.8Ni7.5Co19.7 to Al71.1Ni18Co10.9 and to an Al71.3Ni13.4Co15.3 mono-quasicrystal The measurements were carried out in the temperature range from 290 K up to 1220 K for measuring frequencies between 0.1Hz and 10 kHz. A loss maximum of Debye type is observed at ≈ 700 K (2Hz) for both the I-phase and the bCo-phase, which is attributed to local rearrangement of point defects. The activation enthalpy of the peak of H = 1.9 - 2.4 eV is in the range of values obtained from tracer diffusion experiments. This indicates that local defect rearrangement and self diffusion are governed by the same atomic diffusion process.. A high temperature viscoelastic damping background is only observed in polycrystalline samples with H = 2.4 – 3 eV. The background is assigned to viscolealastic relaxation based on intergranular diffusion.