AlCuFe quasicrystals: Local electronic properties of these new industrial materials

We present room temperature 57Fe Moessbauer centre (isomer) shift and electric field gradient (EFG) results in the Al100-x-yCuxFey icosahedral-quasicrystalline (i-) and crystalline phases. We have investigated the local electronic properties and atomic order along the existence domains of the quasicrystalline and approximant phases given by two close-lying parallel lines in the concentration diagram: the I-line, where the quasicrystal is stable, and the A-line, where the rhombohedral approximant is stable, and other high-order approximants (orthorhombic and pentagonal) as well as the quasicrystal phase are metastable. We have also studied a series of intermediate concentrations situated between the I- and A-lines retained in the metastable i-phase by quenching. It is found that the centre shift and EFG are linearly correlated to each other over the range of compositions and structures for both the I- and A-lines as well as the intermediate samples. This correlation results from systematic changes in the orbital occupations on Fe atoms with composition.We have investigated as well the new low-order cubic approximant phase containing Si. The results for this phase fall near to but not on the correlation line indicating small changes in the atomic binding as compared to the i- and high order approximant phases. In addition, we have studied several non-approximant phases which lie close to these phases in composition. The results for the non-approximant structures do not fall near the correlation line, indicating very different atomic binding