Thermoelectric Properties of Bi-Sb-Te-X Compounds Prepared by MA-PDS Method
- PDF / 106,891 Bytes
- 5 Pages / 595 x 842 pts (A4) Page_size
- 90 Downloads / 207 Views
Thermoelectric Properties of Bi-Sb-Te-X Compounds Prepared by MA-PDS Method Yong-Ho Park and LIU Xue-Dong National Institute of Advanced Industrial Science and Technology (AIST Tohoku) Sendai 983-8551, Japan ABSTRACT A great potential for further improving the room-temperature figure of merit (Z) has been identified by dispersing a small fraction of Ag in the (Bi0.25Sb0.75)2Te3 alloy. The maximum Z of 3.41×10-3K-1, 17% higher than that of the unadded, is attained at 0.02wt% Ag. Addition of BN, either alone or in combination with Ag, however, does not generate a favorable figure of merit. INTRODUCTION Recent studies [1-3] have revealed that powder processing is a viable synthesis route for producing Bi2Te3-based thermoelectric (TE) polycrystals that exhibit both great mechanical strength and improved thermoelectric performance compared with the single-crystal counterparts. In order to achieve more widespread applications of the current Bi2Te3-based TE materials, attempts were made to further increase the figure of merit (Z). Based on a theoretical effort, Fleurial [4] predicted that dispersion of ultrafine inert inclusions in the ptype Bi2Te3-based alloys could improve the figure of merit by 15-20% at 200-300K. The dispersed fine particles act as effective scattering agents for phonons and thus substantially reduce the lattice thermal conductivity. In the dispersing study of ceramic BN and WO3 particles in the (Bi0.2Sb0.8)2Te3 alloy, Lee et al. [5] reported a decreased Z with the increasing volume fraction of the added ceramic particles. Z degradation was due to the fact that the increment in the electrical resistivity was much larger than the reduction in the thermal conductivity. Ohnaka et al. [6] suggested that the figure of merit might be enhanced by adding fine, electrically conductive particles that has no reaction with the matrix. Thus far, little work has been done on this study in the Bi2Te3-based semiconductors. In the present study, we selected (Bi0.25Sb0.75)2Te3 (at.%) as the mother alloy. Our research is devoted to the addition of metal Ag or ceramic BN or both, in order to explore the potential for further increasing the room-temperature figure of merit of the mother alloy. EXPERIMENTAL DETAILS Bulk polycrystalline samples were prepared by mechanical alloying followed by pulse discharge sintering (MA-PDS). 5N elemental powders of bismuth (-80mesh), tellurium (100mesh) and antimony (-100mesh) as well as Ag (∼2µm diameter, >99.9%) and BN (∼10µm diameter, 99%) additive powders were used as starting materials for mechanical alloying (MA). MA was carried out in a vibratory ball mill under the vibration frequency of 25Hz. The stainless steel vial with ZrO2 lining and ZrO2 balls of 15.5mm in diameter were utilized. The powders in the desired composition were pre-mixed and loaded into the vial at the ball-topowder mass ratio of 75:1. MA was conducted in argon atmosphere for 200h without interruption. All the powder handling was done in an argon-filled glove box, in which the oxygen level was kept below 5ppm, to
Data Loading...
