Relationship of phason strain and electronic properties in icosahedral Al–Pd–(Re,Mn) and Al–Cu–Os

Single-phase icosahedral Al70.5Pd21(Re,Mn)8.5 and Al65Cu20Os15 samples have been studied in order to find a relationship between electronic localization and structural properties of icosahedral quasicrystals. Annealed at high temperatures (HT), e.g. 940°C, the Al–Pd–Re samples exhibit a behavior which can be described as nearly localized, while annealed at low temperatures (LT), e.g. 600–640°C, localization has been observed. Similar observations have been made for icosahedral Al–Cu–Os. Accordingly, Al–Pd–Re and Al–Cu–Os can be considered as model systems for this type of investigation. Performing transmission electron microscopy measurements, we have observed and quantified the phason strain in these samples: For the two model systems the HT-states are closer to a perfect icosahedral state containing some random phason strain, in the LT-states we observed a strongly phason-perturbed i-phase. Additionally, the influence of chemical disorder was studied by the addition of Mn into icosahedral Al–Pd–Re.