Münster 1999 – scientific programme

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M: Metallphysik

M 3: Quasikristalle I

M 3.6: Talk

Monday, March 22, 1999, 12:00–12:15, S 9

Phonons and Phasons in Quasicrystals: Quasielastic Mössbauer Experiments in i-Al-Cu-Fe — •R.A. Brand and J. Voß — Department of Physics, Gerhard-Mercator-University Duisburg

We present new results on the dynamical properties of iron in i-Al-Cu-Fe quasicrystals. We have studied icosahedral Al₆₂Cu_25.5 ⁵⁷Fe_12.5 using quasielastic Mössbauer spectroscopy for T  ≤  1100 K. We find that the Debye Waller factor f(T) of the central elastic (quadrupole-split) line decreases abruptly below the Debye result f_D(T) for T  >  600 K. But there is an additional quasielastic signal which correlates with the appearance of this anomaly. This is due to atomic motion of the Fe atoms from phason jumps. The electric field gradient shows a different dependence on temperature, decreasing only slowly up to about 800 K, but then much faster. These results give the temperatures where phason motion (≥ 600 K), and then vacancy motion (≥ 800 K), strongly affect the Mössbauer spectrum.

These results will be compared to new results for the vibrational density of states for iron atoms in i-Al-Cu-Fe.