Dynamics of long-wavelength phason fluctuations in the i-Al-Pd-Mn quasicrystal
Résumé
We report on the dynamics of phason modes with propagation vector q along (-, 1, 0) in the i-Al-Pd-Mn icosahedral quasicrystal, measured between room temperature and 650°C, using the X-ray Intensity Fluctuation Spectroscopy technique (XIFS). Up to 500°C, the auto-correlation function corr (q, t) displays almost no time evolution as expected for frozen-in phason fluctuations at low temperature. At higher temperatures, corr (q, t) follows a single exponential time decay from which the characteristic time c(q) is extracted. These results are compared with the expected shape of corr (q, t) as derived from the expressions of the eigenvalues and eigenvectors of the phason dynamical matrix. In agreement with the hydrodynamic theory of quasicrystals which predicts phasons with diffusive character, we find that c(q) varies linearly with q-2 at 650°C. The corresponding diffusion coefficient is 2.2( 0.5)10-18 m².s-1 and the activation energy is estimated around 2.3( 1) eV.
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