CONCENTRATION-DEPENDENCE OF THE LOCAL ELECTRONIC-PROPERTIES OF ALCUFE QUASI-CRYSTALS AND CRYSTALLINE APPROXIMANTS

The icosahedral quasicrystal Al100-x-yCuxFey is stable at low temperature only along a narrow line-like domain around Al62Cu25.5Fe12.5. In a nearby narrow line-like domain parallel to the first, the icosahedral structure transforms at low temperatures into a stable rhombohedral approximant (3/2) phase. For the first time, we have investigated the-local electronic properties and local order along these stability lines, using both Fe-57 Mossbauer and Al-27 NMR spectroscopy. We show that the local properties (as given by the Fe-57 central line shift and quadrupole splitting and Al-27 average line shift and line shape) are insensitive to the nature of the long-range order, icosahedral quasicrystal or rhombohedral approximant, at a given composition. In addition, a new pentagonal approximant found along the rhombohedral line gave the same results as the quasicrystal for the same composition. The changes in the electronic properties along the two stability lines are about a factor of three smaller than the changes from the stable icosahedral to the stable rhombohedral domains although there is a factor of three larger change in concentration, These observations are consistent with the constant value of the number of electrons per atom (referred to as e/a) along the lines, and changes in e/a between them, as estimated from the alloy composition.