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 h ave been studied in order to find a relationship between electronic localiz ation and structural properties of icosahedral quasicrystals. Annealed at h igh temperatures (HT), e.g. 940 degreesC, the Al-Pd-Re samples exhibit a be havior which can be described as nearly localized, while annealed at low te mperatures (LT), e.g. 600-640 degreesC, localization has been observed. Sim ilar 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 inve stigation. Performing transmission electron microscopy measurements, we hav e observed and quantified the phason strain in these samples: For the two m odel systems the MT-states are closer to a perfect icosahedral state contai ning some random phason strain, in the LT-states we observed a strongly pha son-perturbed i-phase. Additionally, the influence of chemical disorder was studied by the addition of Mn into icosahedral Al-Pd-Re. (C) 2000 Elsevier Science B.V. Al rights reserved.