Thermoelectric properties of binary Cd-Yb quasicrystals and Cd6Yb

The thermoelectric properties, including electrical resistivity ~r!, Seebeck coefficient (S), and thermal conductivity ~k! on binary icosahedral Cd-Yb quasicrystals and Cd6Yb are investigated. The Cd-Yb quasicrystals have a room-temperature ~RT! resistivity value of about 200 ~mV cm!, however, the temperature-dependent resistivity is sensitive to a small composition change in these compounds. For all studied samples, Seebeck coefficients are positive and small (;10 mV/K at RT!. Upon cooling, S decreases quasilinearly, indicative of a metallic diffusion behavior, and then develops a broad phonon drag peak at around 40 K. The temperature characteristic of thermal conductivity k of Cd-Yb quasicrystals shows a most peculiar feature in all measured thermoelectric properties. The RT k value ;6 (W/m K) of Cd-Yb quasicrystals is considerably larger than that of conventional ternary counterparts. Such an observation is attributed to the substantial electrical contribution ke (;50%) to their total thermal conductivity, as deduced from the Wiedemann– Franz’s law, and larger lattice thermal conductivity kP due to less chemical disorder present in the binary Cd-Yb quasicrystalline structure. In addition k decreases with decreasing temperature and shows a distinct maximum, a broad maximum, or a plateau at low temperatures, depending on the sample composition. The dimensionless thermoelectric figure of merit (ZT) for Cd-Yb quasicrystals is estimated to be small, on the order of 0.005 at RT. © 2004 American Institute of Physics. @DOI: 10.1063/1.1642282#