Electronic structure and electron transport properties of Mg-Al-Pd quasicrystals and approximant crystals

The electronic structure and electron transport properties were studied of rhombic triacontahedron-type icosahedral (RT-phase) quasicrystals and their 1/1-approximants in a series of Mg86-xAlxPd14 (x=42, 46, 50 and 54) and Mackay-type icosahedral (MI-phase) quasicrystals containing 30 at.% Pd by measuring the low-temperature specific heat, the electrical resistivity, the XPS valence band spectra and Al Kβ SXS emission band spectra. The resisitivity at 300 K increases not only on improvement of the quasicrystallinity in the thermally stable RT-phase but also on transformation to the 1/1-approximant. The resistivity of the MI-phase reaches 700 μΩ cm and is more than three times as large as that of the thermally stable RT-phase. A combination of XPS valence band spectra and the Al Kβ SXS spectra led us to conclude that Al-Pd covalent bonding occurs in all samples studied and becomes substantial in the MI-phase. The Al 3p electrons are depleted to form the bonding states with Pd 4d electrons and the resulting reduction in Al 3p electrons at the Fermi level is most probably responsible for the large resistivities of the three relevant phases. ((orig.))