Valence band structure and electron transport properties in rhombic triacontahedron and Mackay icosahedral types of Al-Mg-Pd and other quasi-crystals

The valence band structure of both rhombic triacontahedron (RT) and Mackay icosahedron (MI) types of quasi-crystal (QC) is studied by means of X-ray photoemission spectroscopy and the Al K and Pd L beta 2,15 soft X-ray spectroscopy techniques. Information about the density of states at the Fermi level E F is supplemented by the data on the electronic specific-heat coefficient. The Hall coefficient is also studied. The Al-Mg-Pd, Al-Mg-Zn and Al-Mg-Cu QCs are selected as representative of the RT-type QCs and Al-Mg-Pd, Al-Ru-Cu and Al-Re-Pd as representative of the MI-type QCs. The valence band structure of the RT-type QCs is characterized by a narrow d band in the middle of the valence band and a quasi-free-electron-like smooth density of states in the vicinity of E F . On the other hand, the d states of the transition-metal elements are more widely spread in the MI-type QCs. The depletion minimum in the Al 3p electron distribution occurs at the binding energies 3-5 owing to the interaction with the d states of the late-transition-metal elements. The presence of the pseudo-gap across E F has been confirmed in both RT- and MI-type Al-Mg-Pd QCs. We propose also that the effective carrier concentration derived from the Hall coefficient may be used as a universal parameter for both RT- and MI-type QCs in place of the conventionally used electron concentration per atom. We found that the resistivity and electronic specific-heat data exhibit universal relationships when plotted as a function of the effective carrier concentration. From this we conclude that either electrons or holes dominate at E F in most RT- and MI-type QCs studied so far. Exceptions to this will be those whose Hall coefficient is extremely small and changes its sign with temperature.