Positron-annihilation studies of stable Al-based icosahedral quasicrystals

Abstract

The positron-annihilation lifetime spectra in the Al-Pd-Re alloy system, the positron-annihilation Doppler-broadening spectra by slow variable monoenergetic positron beam in ${\mathrm{Al}}_{70.7}{\mathrm{Pd}}_{21.34}{\mathrm{Re}}_{7.96}$ and ${\mathrm{Al}}_{71.5}{\mathrm{Pd}}_{20.3}{\mathrm{Mn}}_{8.2}$ alloys, and positron-annihilation lifetime spectra by slow positron beam in ${\mathrm{Al}}_{71.5}{\mathrm{Pd}}_{20.3}{\mathrm{Mn}}_{8.2}$ were measured. These measurements indicate that every sample contains a dense distribution of structural vacancy-type sites. This result is consistent with our previous expectation of the relationship between the presence of vacant centers in clusters and the stability of icosahedral quasicrystals. Furthermore, the structural vacancy densities in icosahedral quasicrystals of ${\mathrm{Al}}_{70.7}{\mathrm{Pd}}_{21.34}{\mathrm{Re}}_{7.96}$ and ${\mathrm{Al}}_{71.5}{\mathrm{Pd}}_{20.3}{\mathrm{Mn}}_{8.2}$ have been estimated to be $7.7\ifmmode\times\else\texttimes\fi{}{10}^{20}$ and $5.0\ifmmode\times\else\texttimes\fi{}{10}^{20}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$ respectively.