The internal friction was measured for an Al-Pd-Mn icosahedral phase (i-phase) and its 1/1 and 2/1 approximant phases in an Al-Pd-Mn-Si system in a forced flexural-oscillation mode in a frequency range of 0.05–20 Hz and a temperature range of 300–873 K. For the i-phase, large and small absorption peaks were observed with $Q^{-1}\approx 1.3\times {10}^{-2}$ and $8\times {10}^{-4}$, respectively. These two peaks were absent for the 1/1-phase, which showed two other peaks instead. The 2/1-phase exhibited the features of both the i and 1/1-phases; it showed two peaks of the i-phase and one of the two peaks of the 1/1-phase. All the observed peaks were of the thermally activated relaxation type, and their activation enthalpies and frequency factors were evaluated. The larger peak of the i-phase, which was absent for the 1/1-phase and present with a much reduced intensity for the 2/1-phase, was shown to result from a relaxation process involving collective atomic motion. Collective and correlated phason jumps were discussed as a possible mechanism for it. It was speculated that the other peaks observed only for the approximant phases are due to Zener relaxations by the reorientation of atom pairs involving Si.

• Received 11 November 2009

DOI:https://doi.org/10.1103/PhysRevB.80.224204

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