Atomic defects in quasicrystals:: an approach with positron annihilation spectroscopy and time-differential dilatometry

Atomic defects have been studied in Al-Pd-Mn and Zn-Mg-Ho icosahedral quasicrystals by means of positron annihilation spectroscopy and time-differential dilatometry. In addition, the first in situ positron lifetime measurements on Al-Pd-Mn quasicrystals at high temperatures are performed. In the time-differential dilatometry studies, after fast cooling at high temperatures an anomalous time-dependent isothermal expansion of the specimen was observed. If this length change is attributed to atomic defects the defect formation and the migration can be studied. Positron lifetimes could be derived for icosahedral Al70.2Pd21.3Mn8.5 and icosahedral Zn61Mg28Ho11 with 214 and 212 ps, respectively. These lifetimes are ascribed to structural vacancies in these quasicrystalline systems, which are supported, by electron irradiation and long-term annealing experiments. (C) 2000 Elsevier Science B.V. All rights reserved.