Electrical properties of the binary icosahedral quasicrystal and its approximant in the Cd–Yb system

Electrical resistivity, magnetoresistance, and specific heat measurements have been performed for the binary icosahedral Cd5.7Yb and its cubic approximant Cd6Yb. The resistivity of both the icosahedral phase (i-phase) and the approximant is found to show a rather metallic behavior with a large positive temperature coefficient of the resistivity (TCR) below 200–300 K followed by leveling-off at low temperatures below 10 K. For the approximant, we observe a stepwise change of the resistivity at 110 K which is due to a phase transition. Giant magnetoresistance as high as 200% at 9 T below 4.2 K is observed for the i-phase and the electronic specific heat coefficient γ is found to be extraordinary large in both alloys, i.e., 2.87 mJ/(mole K2) for the i-phase and 7.60 mJ/(mole K2) for the approximant. Such large γ values may be attributed to the Yb-derived states at the Fermi level. Furthermore, the Debye temperatures (ΘD) are very low and almost the same for both alloys, i.e., 142 and 144 K, respectively, which are indeed the lowest values ever reported in i-phases and approximants. The metallic character of the binary i-phase implies that the negative TCR is not necessarily a consequence of the quasiperiodicity.