ELECTRONIC-STRUCTURE, ELECTRON-TRANSPORT PROPERTIES, AND RELATIVE STABILITY OF ICOSAHEDRAL QUASI-CRYSTALS AND THEIR 1 1 AND 2/1 APPROXIMANTS IN THE AL-MG-ZN ALLOY SYSTEM/

Electronic properties of icosahedral quasicrystals have been often dis cussed on the basis of the valence band structure of their cubic 1/1 a pproximants for which the band calculations are available. However, th ere exists no a priori justification for the neglect of the difference between the quasicrystal and its lowest-order approximant. Studies of the hierarchy dependence of the electronic structure and electron tra nsport properties in a given system are, therefore, highly important. The Al-Mg-Zn system is chosen in this work, since a thermally stable q uasicrystal and its 2/1 and 1/1 approximants can be prepared. Electron ic properties, which include x-ray photoemission spectroscopy and soft x-ray spectroscopy valence band structure, the electronic specific he at coefficient, the resistivity, and the Hall coefficient, have been m easured. We conclude that the electronic structure and electron transp ort properties of the thermally stable quasicrystal are substantially different from those of the 1/1 approximant but are essentially identi cal to those of the 2/1 approximant. It is also shown that the thermal ly stable icosahedral quasicrystal, the 2/1 and 1/1 approximants are c ompeting among them as the Hume-Rothery electron phases, in which an e lectron concentration e/a and a composition ratio X(Mg)/(X(Al) + X(Zn) ) of a larger Mg atom over smaller Al and Zn atoms serve as two critic al factors to decide their most stable compositions.