Effect of Mechanical Deformation on Thermoelectric Properties of p-Type(Bi0.225Sb0.775)2Te3Alloys

Sung-Jin Jung,Dow-Bin Hyun,Hyung-Ho Park,Seung-Hyub Baek,Seong Keun Kim,Jin-Sang Kim

doi:10.1155/2013/868540

Abstract

The effect of mechanical deformation and annealing on thermoelectric properties of p-type (Bi0.225Sb0.775)Te3was performed. The ingots were prepared by melting, followed by quenching method using source materials with compositions of (Bi0.225Sb0.775)2Te3. Rectangular shaped specimens (5×5×12 mm3) were cut from ingots and then cold-pressed at 700 MPa for 2 to 20 times by changing the press direction perpendicular to previous one. The cold-pressed samples have been annealed in a quartz ampoule at 573 K. The grain size of the samples was controlled by the number of cold-pressing process and annealing time. Fine grain structure with a grain size of not more than 10 μm is obtained in highly deformed samples. The Seebeck coefficient of the deformed samples were gradually increased with annealing and converged to the similar value of about 225 μV/K after 30 hrs. The small grain size in highly deformed sample enables a rapid increase of Seebeck coefficient with annealing time (~2 hrs.), indicating that the thermal energy needed to recrystallize in highly deformed specimens is lower than that in low deformed specimens.Zvalues are rapidly increased with annealing time especially in highly deformed alloys, and converge to about3.0×10−3/K at room temperature. A higher thermoelectric performance could be expected by the optimization of composition and microstructural adjustment. The present study experimentally demonstrates a simple and cost-effective method for fabricating Bi-Te-based alloys with higher thermoelectric performance.

Highlights

Bi2Te3-related compounds such as solid solutions of Bi2Te3 and Sb2Te3 have been widely studied over the past decades due to their excellent properties for use in thermoelectric cooling and power generation near the room temperature [1,2,3]
High density of dislocation as well as the reduction of grain size may be expected in our cold-pressed samples
The grain size of cold-pressed samples was controlled by the number of cold-press processing and annealing times

Summary

Introduction

Bi2Te3-related compounds such as solid solutions of Bi2Te3 and Sb2Te3 have been widely studied over the past decades due to their excellent properties for use in thermoelectric cooling and power generation near the room temperature [1,2,3]. Thermoelectric nanostructures can be produced by many techniques, such as hydrothermal methods [7], wet chemical reactions [8], and ball milling [2, 4]. Conventional ball milling has been employed to produce large quantities of fine particles with a size of one to several microns and this process can be readily scaled up for commercial use at reasonable cost. To improve the mechanical and electrical properties of the composites, the cold-pressing should be followed by sintering at appropriated temperatures. As a powder preparation method, high energy ball milling is generally used with source materials of crystalline Bi-Sb-Te alloy ingots which are prepared by zone melting and Bridgman methods [5, 9, 11, 13]. Thermoelectric properties are discussed on the point of view of microstructural evolution of cold-pressed sample with annealing

Experimental Procedures

Results and Discussion

Conclusions