STUDY OF AL-CU HUME-ROTHERY ALLOYS AND THEIR RELATIONSHIP TO THE ELECTRONIC-PROPERTIES OF QUASI-CRYSTALS

The stability of quasicrystals is related to the Hume-Rothery mechanis m known to take place in many intermetallics, especially Al-Cu alloys. In order to assess to what extent the electronic density of states in aperiodic Al-Cu-Fe compounds is sensitive to Hume-Rothery stabilizati on, we present experimental measurements by soft x-ray emission and ab sorption spectroscopies of the aluminium electronic states in a series of Al-Cu crystalline compounds. Some of them, like icosahedral Al-Cu- Fe, are characterized by nearly spherical Brillouin zones. We observe the opening of a narrow but definite pseudo-gap in such Al-Cu compound s. We point out a strong interaction between Cu d states and the Al st ates in the middle of the valence band which is well described by a Fa no-like effect. Some other characteristic features of our spectra are interpreted on the basis of band structure calculations. A comparison to previous data published for quasicrystalline and approximant phases stresses the importance for the stability of these compounds of spd h ybridization at the Fermi level. It also leads to the conclusion that the effect of Hume-Rothery interaction is dramatically enhanced by the hierarchical structure of quasicrystals rather than by the almost sph erical shape of the Brillouin zone.