Electronic distributions and pseudo-gap in quasicrystalline decagonal Al65Cu15Co20 and Al70Co15Ni15 alloys

Electronic state distributions of decagonal Al65Cu15Co20 and Al70Co15Ni15 quasicrystals have been investigated by experimental means using the soft-x-ray spectroscopy technique complemented by photoemission spectroscopy measurements. In both quasicrystals, interaction is shown within an energy range of 2 eV below the Fermi level between the Al states and either the Co 3d states or both the Ni 3d and the Co 3d states. In Al65Cu15Co20, the Cu 3d states are observed in the middle of the occupied band. The formation of a significant pseudo-gap at the Fermi level is shown in the Al 3p and 3s-d distributions of these alloys. The comparison with available photoemission data an Al65Cu20Co15 and Al70Co15Ni15 samples shows good agreement in the energy positions of Cu, Co and Ni occupied states. The results for Al65Cu15Co20 are compared with calculations of densities of states for two models of the Al-Co-Cu decagonal quasicrystals. Very good agreement between experiment and one of these calculations is found for the Al distributions. For Al70Co15Ni15, fair agreement between the present results and data for crystalline Al5Co2 is shown. The Al p and Ni s-d unoccupied states are considered as well in Al70Co15Ni15. It is suggested that a slight charge transfer may occur from Al to Ni in this sample and that most of the Al p unoccupied states presumably occur from the contribution of the quasiperiodic planes in this specimen.