CRYSTALS AND QUASICRYSTALS: ELECTRONIC STRUC-TURE VERSUS ATOMIC STRUCTURE. Esther Belin-Ferre, LCPMR (URA CNRS 176) and GDR CINQ, 11 rue Pierre et Marie Curie, 75 231 Paris Cedex 05, France, T.( 33) 1 44 27 66 20, F.(33) 1 44 27 62 26, e-mail : belin@ccr.jussieu.fr, Jean Marie Dubois, LSG2M (CNRS 159) and GDR CINQ, EMN, Parc de Saurupt, 54042 Nancy Cedex , France, T.(33) 83 58 41 98, F.(33) 44 27 62 26, e-mail : dubois@mines.u-nancy.fr

The electronic structure of all solids is closely related to their atomic structural arrangement. In this paper, we compare experimental data representative of the electronic structure of quasicrystals and of related crystalline phases showing however different medium and long range orders. Our aim is to investigate to which extent the electronic structure of quasicrystals exhibits a fingerprint that could arise from topological specificity.

Measurements have been carried out using Soft X-ray Emission and Absorption Spectroscopies and X-ray Photoemission Spectroscopy techniques. Combining these techniques allows us to obtain separately occupied and empty partial (s,p,d..) electronic distributions around each atomic site of the solid, adjusted to the binding energy scale

We present here descriptions of occupied and unoccupied bands in various binary and ternary crystalline Al intermetallic alloys as well as in Al based icosahedral and decagonal quasicrystals. We describe and discuss the electronic interactions that take place in these alloys. We emphasize that the study of the Al electronic distributions of p character gives direct evidence of the progressive appearance of non metallic character of the alloy with increasing the degree of icosahedral order. In icosahedral quasicrystals of high structural quality the Al p electronic structure is reminiscent of that of a semi-conductor. This effect is in strong relation with the increase of resistivity in the same alloys. A discussion of the results is proposed in connection with a recent model based upon hierarchically arranged clusters of atoms (the so-called McKay icosahedra).