Cerium Doped Bismuth Antimony
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Cerium Doped Bismuth Antimony
Kevin C. Lukas1, Huaizhou Zhao1, Ryan L. Stillwell2, Zhifeng Ren1, Cyril P. Opeil1 1
Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, U.S.A.
2
National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 323064005, USA
ABSTRACT Bismuth-Antimony alloys have been shown to have high ZT values below room temperature, especially for single crystals. For polycrystalline samples, impurity doping and magnetic field have proven to be powerful tools in the search for understanding and improving thermoelectric performance. Nanopolycrystalline Bi0.88Sb0.12 doped with 0.05, 0.5 and 3 % Ce were prepared by ball milling and dc hot pressing techniques. Electrical resistivity, Seebeck coefficient, thermal conductivity, carrier concentration, mobility, and magnetization are measured in a temperature range of 5-350 K and in magnetic fields up to 9 Tesla. The effects of Ce doping on the thermoelectric properties of Bi0.88Sb0.12 in zero magnetic field are discussed. INTRODUCTION Bismuth-Antimony alloys are known to have some of the best thermoelectric properties below room temperature, specifically single crystals [1-3]. The problem with single crystals is that they are difficult to fabricate and they are mechanically weak making them impractical for commercial use. Polycrystalline BiSb alloys have been fabricated via several different methods [4-7], however all polycrystalline samples have thermoelectric properties that are inferior to single crystal samples. In order to enhance the thermoelectric properties of polycrystalline BiSb, dopants can be added [8-10]. In our previous report, we demonstrated an increase in ZT for Bi0.88Sb0.12 doped with Holmium [11]. In this report we present the thermoelectric transport properties for Bi0.88Sb0.12 doped with 0.05, 0.5, and 3 % Cerium. EXPERIMENTAL DETAILS The proper stoichiometric amounts of elemental Bismuth (Alfa Aesar 99.999%), Antimony (Alfa Aesar 99.999%) and Cerium (Alfa Aesar 99.99%) were melted in quartz tubes at 450 oC for 3 hours then quenched in water. The ingot was then ball milled for five hours in a high energy ball mill from which the powder was taken and hot pressed at 200 oC in a manner previously described [11]. XRD measurements were performed on as pressed samples using a Bruker AXS XRD to show the materials were single phase. The magnetic susceptibility (χ) was measured using a Physical Properties Measurement System (PPMS) from Quantum Design. Samples were cut into 1 x 2 x 12 mm3 dimensions to measure the Hall coefficient (RH) and 2 x 2 x 4 mm3 dimensions for measurements of electrical resistivity (ρ), thermal conductivity (κ), and the Seebeck Coefficient (S). All transport measurements were made perpendicular to the face of the disk, or pressing direction, using a PPMS.
RESULTS AND DISCUSSION Figure 1a shows XRD images of the 0, 0.05, 0.5, and 3 % Ce doped Bi0.88Sb0.12 samples. It can be seen that within the resolution of the machine, the samples are all single phase with no secondar
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