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 Ma ckay icosahedron (MI) types of quasi-crystal (QC) is studied by means of x-ray photoemission spectroscopy and the A1 K and Pd Lbeta2,15 soft x-ray spectroscopy techniques. Information about the density of state s at the Fermi level E(F) is supplemented by the data on the electroni c 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 o f E(F). On the other hand, the d states of the transition-metal elemen ts 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 eV owing to the interaction with the d states of the late-transition-met al elements. The presence of the pseudo-gap across E(F) has been confi rmed in both RT- and MI-type Al-Mg-Pd QCS. We propose also that the ef fective carrier concentration derived from the Hall coefficient may be used as a universal parameter for both RT- and MI-type QCS in place o f the conventionally used electron concentration per atom. We found th at the resistivity and electronic specific-heat data exhibit universal relationships when plotted as a function of the effective carrier con centration. From this we conclude that either electrons or holes domin ate 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 chang es its sign with temperature.