ALP CONDUCTION STATES IN QUASI-CRYSTALLINE AL-CU-FE ALLOY AND RELATED-COMPOUNDS

We have examined in details the Al p conduction states as well as the Al 3p valence distributions in quasi-crystalline Al62Cu25.5Fe12.5, rhombohedral approximant R-Al62.5Cu26.5Fe11 and tetragonal omega-Al7Cu2 Fe phase. A significant issue is that, in a wide energy range beyond the Fermi level, there is a noticeable decrease of the density of the Al p conduction states in the quasi-crystalline material. Conversely, the conduction Al p band is very much different in metallic aluminium, whereas the situation is found intermediate in the omega- and R-compounds. We point out that a major difference between the icosahedral quasi-crystalline alloy and its rhombohedral approximant is shown by the conduction electronic distributions in contrast with many other properties which, as is well known, present no significant difference. Such a behaviour may be ascribed in part to the progressive disappearance of the crystalline periodic order. Our result is the first experimental evidence in favour of theoretical predictions made elsewhere that the electronic band structure of approximant phase and merely of quasi-crystals consists in a succession of numerous spikes and gaps.