| Popis: |
For studying atomic vacancies in quasicrystals the specific technique of positron annihilation spectroscopy has been employed. In quasicrystals and approximants of the Al–Pd–Mn and the Zn–Mg–Ho systems structural vacancies in the concentration range of 10 −3 have been observed. We perform the first in-situ measurements of the positron lifetime at high temperatures, where the formation of thermal vacancies in i-Al 70.2 Pd 21.3 Mn 8.5 can be observed directly. The annealing behavior of quenched-in vacancies, which coincide with the data from earlier time differential dilatometry studies after fast temperature changes, gives access to the vacancy migration properties and kinetics in quasicrystals. From the coincident measurement of the Doppler broadening of the positron-electron annihilation photon line at ambient temperatures, we deduce that the vacancies observed in i-Al 70.2 Pd 21.3 Mn 8.5 are predominantly located in an Al rich environment. Since high-temperature processes such as diffusion, plasticity and structural phase transformations, are strongly influenced by thermal vacancies and their kinetics, the present experiments can provide information on these processes. |
Full Text from ScienceDirect