engleski

Physical Properties of the Bergman Phase Mg32(Al, Zn)49

We report results of the investigation of the physical properties of a complex intermetallic compound, namely the Bergman phase Mg32(Al, Zn)49 whose giant cell contains 162 atoms. The atoms are arranged in clusters with poly-tetrahedral order with icosahedrally coordinated environment. The sample, prepared from a monocrystalline ingot grown using the Czochralski technique, was cut into a rectangular prism with its long axis parallel to the (100) direction. The chemical composition was determined to be in the range of the Bergman phase and it was checked to be a single phase using backscattering electron image experiments. The electrical resistivity data, in the 4 K to 300 K temperature interval, show a behavior similar to that of a low-resistivity non-magnetic amorphous alloy. Magnetic susceptibility measurements show that the sample is a Pauli paramagnet with a significant Landau diamagnetic orbital contribution. This, together with the NMR Knight-shift measurement, suggests that the observed small positive temperature dependence of the susceptibility arises from the mean-free-path effect on the orbital susceptibility. Thermal conductivity measurements between 8 K and 300 K have led to the conclusion that electronic conductivity dominates over lattice conductivity at room temperature so that the Bergman phase is in-between regular metals and quasicrystalline compounds. Thermopower results, between 4K and 300 K, show a negative value for the Seebeck coefficient which indicates that electrons are dominant charge carriers. Our results indicate that, for the Bergman phase, the high structural complexity does not imply the complexity of the electronic structure.

complex metallic alloys; Al_2Mg_3; electrical resistivity; thermopower; thermal conductivity; magnetic susceptibility

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