Positron-annihilation study of equilibrium defects ...

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Title Positron-annihilation study of equilibrium defects in Al-Cu-Fe face-centered-icosahedral quasicrystals
Author(s) Derek W. Lawther, R. A. Dunlap
Journal Physical Review B
Date 1994
Volume 49
Issue 5
Start page 3183
End page 3189
Abstract In situ Doppler-broadening temperature scans and room temperature positron-lifetime measurements are reported for Al63CU25Fe12, Al62.5CU25Fe12.5, Al62CU25.5Fe12.5, and Al62Cu22.8Fe15.2 face-centered-icosahedral (FCI) quasicrystalline samples. Quenched-in disorder has been observed and found to anneal out of the samples above 200 degrees C. A quasicrystal-to-microcrystal phase transition has been observed in two of the samples (Al63Cu25Fe12 and Al62Cu22.8Fe15.2), indicating an instability of the FCI phase at low temperatures. No such transition is observed in the other two samples (Al62.5CU25Fe12.5 and Al62Cu25.5Fe12.5). It is shown that intrinsic structural vacancies, possessing only Al-atom nearest neighbors, exist in both the microcrystal and FCI phases and act as saturation traps for the positrons. At similar to 200 degrees C, thermal activation of dynamic Al-atom phasons in the FCI phase results in distortions of the intrinsic structural vacancies as the nearest neighbor Al atoms begin to hop within double-well potentials. At higher temperatures (525-750 degrees C depending upon the sample stoichiometry) dynamic Cu-atom phasons are activated and observed to coincide with the onset of plasticity in the FCI phase.

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