engleski

Phonon scattering in quasicrystalline i-Al72Pd19.5Mn8.5: A study of the low-temperature thermal conductivity

In this work, we have analyzed the thermal conductivity of an icosahedral quasicrys- tal i -Al72Pd19.5Mn8.5 in a temperature range between 0.4 K and 300 K. Tha analysis was made in frames of two models: a Debye model (which implies the quadratic den- sity of vibrational states and the existence of acoustical phonons), and the model of the harmonic approximation with non-quadratic density of vibrational states. The results of the Debye model employed for two temperature regions, T < 40 K and T < 1K, are not compatible to each other. Contrary to T < 1 K-region, fit T < 40 K tunneling states are not present in fit result, although there exist a number of experimental evidences which intrinsically relate the quasicrystal struc- ture and tunneling states. The fit of the experimental data to the harmonic model with non-quadratic vibrational density of states points out the phonon scattering on the tunneling states. In all cases phonon scattering on structural defects of the stacking-fault type resulted from fits. TEM experiment indeed showed the existence of stacking-fault defects, with the number of stacking faults of the same order of magnitude as that calculated by the fitting procedures.

quasicrystals; heat conduction; scanning and transmission electron

This work was supported in a part by the 6th Framework EU Network of Excellence 'Complex Metallic Alloys' (Contract No. NMP3-CT-2005-500140)