• PDF / 225,810 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 42 Downloads / 223 Views

DOWNLOAD

REPORT

---

Thermoelectric Properties of Eu-doped CoSb3 G. A. Lamberton, Jr.1, R. H. Tedstrom1, Terry M. Tritt1, and G. S. Nolas2 1 Department of Physics and Astronomy, Clemson University, Clemson, SC U.S.A. 2 Department of Physics, University of Southern Florida, Tampa, FL U.S.A. ABSTRACT Resistivity and thermopower data is presented on Eu-doped CoSb3 skutterudites over the temperature range of 10 K to 700 K. Thermal conductivity is also presented from 10 K to 300 K in order to determine the figure of merit. Eu0.43Co4Sb11.59Ge0.31 and Eu0.42Co4Sb11.37Ge0.50 exhibit an enhanced figure of merit as compared to CoSb3 and Eu0.2CoSb3. Data on a series of Yb-filled CoSb3 is underway and preliminary data is presented. INTRODUCTION Rare earth-filled skutterudites have generated significant interest due to their potential as thermoelectric materials. [1,2,3 ] These materials typically have large power factors and exhibit a reduced thermal conductivity as compared to the parent compositions, with partial void filling yielding the largest reductions. Enhanced reductions are also noted for smaller, heavier filler ions.[4] Though the addition of the filler ion favorably affects the thermal conductivity, the change in carrier concentration due to this additional ion can be detrimental to the electronic properties of the material. In attempt to maintain a favorable carrier concentration of about 1019 – 1020 cm-3, Ge is substituted on the Sb site as an electron acceptor. The measure of a materials effectiveness for thermoelectric applications is the dimensionless figure of merit, ZT = α2σT/κ = α2T/ρκ, with α representing the Seebeck coefficient, σ the electrical conductivity, κ the thermal conductivity, ρ the electrical resistivity, and T the absolute temperature. A recent study of partial void filling CoSb3 with Yb yielded a ZT ~ 1 at 600 K.[5] This paper presents promising results for two Eufilled skutterudites as well and further insight into Yb-doped skutterudite materials. EXPERIMENTAL DETAILS Three Eu-doped samples and four Yb-doped samples of varying composition were studied as part of this investigation. Both systems are CoSb3 based using Ge as an electron acceptor for the charge donated by the filler ion. The samples were bulk, polycrystalline pellets formed by hot-pressing powder in an argon atmosphere. A complete description of sample preparation is available elsewhere.[3,4] Microprobe analysis was performed on these samples and normalized to full occupancy of the metal site in order to arrive at the sample compositions presented. G2.2.1

Resistivity and Seebeck coefficient measurements were carried out concurrently in a custom designed closed cycle helium refrigeration system over a temperature range of 10 K < T < 300 K described elsewhere.[6] Resistivity was measured using the standard four-probe geometry, while sequentially measuring the Seebeck coefficient using a steady state technique. Thermal conductivity measurements were made in a similar apparatus, custom designed for the measurement.[7] Both measurement systems utilize r