Positron-annihilation studies of stable Al-based icosahedral quasicrystals

The positron-annihilation lifetime spectra in the Al-Pd-Re alloy system, th e positron-annihilation Doppler-broadening spectra by slow variable monoene rgetic positron beam in Al70.7Pd21.34Re7.96 and Al71.5Pd20.3Mn8.2 alloys, a nd positron-annihilation lifetime spectra by slow positron beam in Al71.5Pd 20.3Mn8.2 were measured. These measurements indicate that every sample cont ains a dense distribution of structural vacancy-type sites. This result is consistent with our previous expectation of the relationship between the pr esence of vacant centers in clusters and the stability of icosahedral quasi crystals. Furthermore, the structural vacancy densities in icosahedral quas icrystals of Al70.7Pd21.34Re7.96 and Al71.5Pd20.3Mn8.2 have been estimated to be 7.7x10(20) and 5.0x10(20) cm(-3), respectively. [S0163-1829(99)08109- 6].