Effect of rotary-die equal channel angular pressing on the thermoelectric properties of a (Bi,Sb)₂Te₃ alloy

Abstract

A (Bi,Sb) 2 Te 3 alloy powder was sintered via a pulse discharge sintering process followed by a rotary-die equal channel angular pressing (ECAP) process. It was found by x-ray diffraction analysis that the as-sintered material shows preferentially orientated microstructure, which were considerably eliminated by following ECAP processes. Generally, the Seebeck coefficient of the material was reduced by ECAP processing, which was attributed to the increased carrier concentration after the severe plastic deformation. Electrical conductivity increases after ECAP, which was also originated from the increased carrier concentration. The figure of merit of the material in different conditions shows higher value in the transverse direction. In the transverse samples, those after ECAP processing showed increased figures of merit, which reached 3.85 × 10 −3 /K in the material after 4 passes of ECAP.

Thermoelectric and Mechanical Properties of Angular Extruded Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB> Compounds

“…In the last few years, several studies have been made on applying ECAE or similar methods to the bismuth-telluride based materials. [7][8][9] We also had reported that applying the angular extrusion technique with rapidly solidified and stacked foils of bismuth-telluride based material was effective in improving the carrier mobility of the bismuth-telluride based material because of the fine orientated texture that is formed.…”

High-pressure preparation and thermoelectric properties of Bi0.85Sb0.15

“…3 Typically p-Bi x Sb 2Àx Te 3 and n-Bi 2 (Se y Te 3Ày ) are state-of-the-art materials for the 200-400 K temperature range. 4 The product of the figure of merit and temperature, ZT, at 300 K achieved so far is 1.14 for the p-type alloy (Bi 2 Te 3 ) 0.25 (Sb 2 Te 3 ) 0.72 (Sb 2 Se 3 ) 0.03 . 5 At low temperature, ZT of p-type CsBi 4 Te 6 is 0.8 at 225 K, 6 and single crystals of n-type Bi 1Àx Sb x alloys exhibit the optimum thermoelectric performance at 80 K. [7][8][9] Bi and Sb are semimetals, which both exhibit a similar rhombohedral crystal structure (the so-called A7 structure) of space group R 3m.…”

“…Some applications of thermoelectric refrigeration are in the cooling of CCDs, infrared detectors, laser diodes, and CMOS computer processors. [1][2][3][4] Cooling of laser diodes and infrared detectors to temperatures of 100 , T , 200 K would greatly improve the performance and sensitivity. 1,2 Moreover, if the cooling temperature can reach ;90 K, prospects of using thermoelectric refrigeration for superconducting electronics become feasible.…”

“…However, the performance of this material is still far from satisfactory for wider applications because the energy-conversion efficiency is still low. 4 The essence of defining a good thermoelectric material lies in determining the material's figure of merit, Z 5 S 2 s/l, where S is the Seebeck coefficient, s is the electrical conductivity, and l is the thermal conductivity. 3 Typically p-Bi x Sb 2Àx Te 3 and n-Bi 2 (Se y Te 3Ày ) are state-of-the-art materials for the 200-400 K temperature range.…”

Developments in semiconductor thermoelectric materials

“…This bonding becomes a cleavage plane that leads to strength reduction in the single crystal. To overcome the disadvantages presented by single crystals, many synthetic methods were employed to obtain Bi 2 Te 3 -based alloy bulks with higher mechanical strength and good thermoelectric properties; these methods include the Bridgman-Stockbarger method [20], equal channel angular pressing [21], hot pressing [22], hot extrusion [23,24], shear extrusion [25], and physical vapor deposition [26]. Using a two-step spark plasma sintering technique, researchers prepared textured n-type Bi 2 Te 3 with enhanced thermoelectric and mechanical properties; the authors indicated that controlling texture effectively improved the thermoelectric and mechanical properties of Bi 2 Te 3 -based materials [27].…”