Electronic properties of icosahedral quasicrystals in Mg-Al-Ag, Mg-Al-Cu and Mg-Zn-Ga alloy systems

Abstract

The electronic structure and the electron transport properties of sp-electron quasicrystals have been studied, using in total, 20 quasicrystals in the three alloy systems Mg-Al-Ag, Mg-Al-Cu and Mg-Zn-Ga. The authors revealed that the temperature dependence of the electrical resistivity changes its characteristic features with increasing resistivity in the same manner as that in the nonmagnetic amorphous alloys. This is apparently consistent with the generalised Faber-Ziman theory, but this simple model poses difficulties in explaining a definite increase in the resistivity upon improvement in the quasicrystallinity, brought about by the heat-treatment of the Mg_39.5Zn₄₀Ga_20.5 quasicrystal. The Hall coefficient exhibits the sizable temperature dependence when its magnitude deviates from the free electron value, suggesting the important role of the Fermi surface-Brillouin zone interaction. The temperature dependence of the thermoelectric power below 300 K is found to be nonlinear, as opposed to a more linear one in the amorphous alloy. The electronic specific heat coefficient plotted against the electron concentration e/a exhibits a universal trend regardless of the alloy system and decreases with decreasing e/a from the free electron value to about one-third of the free electron value. It is noted that a thermally stable quasicrystal apparently possesses a reduced electronic specific heat coefficient.