Local atomic structure and the valence band structure of the rhombic-triacontahedral quasicrystal, its 1/1 approximant, and the Mackay-icosahedral quasicrystal in the Al-Mg-Pd alloy system

The rhombic-triacontahedral-type quasicrystal ~RT-QC!, its (1/1, 1/1, 1/1) approximant (RT-1/1) and the Mackay-icosahedral-type quasicrystal ~MI-QC! can be formed in the Al-Mg-Pd system. The radial distribution function RDF(r) spectra of the three compounds is derived from neutron diffraction experiments. Powdered x-ray diffraction Rietveld refinement is also carried out to determine the atomic structure of the RT-1/1, and the refined data are converted to the RDF(r). The interatomic distance of the Al-Pd pair in the RT-1/1 and RT-QC is found to be remarkably shortened relative to that calculated from the hard sphere model with Goldschmidt radii. In the MI-QC, the interatomic distance of the Al-Pd pair is further shortened. In addition, the shortening of the interatomic distance is also observed in the Mg-Pd pair. The valence band spectra studied by the x-ray photoemission spectroscopy and soft x-ray spectroscopy clearly show the formation of the bonding and antibonding states associated with the Al-Pd and Mg-Pd atomic pairs in the MI-QC. The results are consistent with the shortening of the interatomic distances derived from the structure analysis. The reason for the possession of the highest resistivity in the MI-QC among the three compounds is attributed to the formation of the covalent bonding between Al-Pd and Mg-Pd atomic pairs. @S0163-1829~98!06841-6#