Abstract
Structural free volumes in the stable quasicrystalline decagonal and adjacent crystalline phases in the Al-Ni-Co, Al-Cu-Co, and Al-Ni-Fe alloy systems were studied by means of positron lifetime measurements. The comparison of different phases and different alloy systems enables an unambiguous assessment of the positron lifetimes in the quasicrystalline state. In each alloy system the quasicrystalline decagonal phase reveals a higher value of the positron lifetime than in the crystalline compounds, which is discussed in terms of different types of structural vacancies or vacancy-type free volumes in the various phases.