Electronic structure, electron transport properties, and relative stability of icosahedral quasicrystals and their 1/1 and 2/1 approximants in the Al-Mg-Zn alloy system.

Abstract

Electronic properties of icosahedral quasicrystals have been often discussed on the basis of the valence band structure of their cubic 1/1 approximants for which the band calculations are available. However, there 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 transport properties in a given system are, therefore, highly important. The Al-Mg-Zn system is chosen in this work, since a thermally stable quasicrystal and its 2/1 and 1/1 approximants can be prepared. Electronic properties, which include x-ray photoemission spectroscopy and soft x-ray spectroscopy valence band structure, the electronic specific heat coefficient, the resistivity, and the Hall coefficient, have been measured. We conclude that the electronic structure and electron transport properties of the thermally stable quasicrystal are substantially different from those of the 1/1 approximant but are essentially identical to those of the 2/1 approximant. It is also shown that the thermally stable icosahedral quasicrystal, the 2/1 and 1/1 approximants are competing among them as the Hume-Rothery electron phases, in which an electron concentration e/a and a composition ratio ${\mathit{x}}_{\mathrm{Mg}}$/(${\mathit{x}}_{\mathrm{Al}}$+${\mathit{x}}_{\mathrm{Zn}}$) of a larger Mg atom over smaller Al and Zn atoms serve as two critical factors to decide their most stable compositions.