J. Seo

Fabrication and thermoelectric properties of p-type Bi0.5Sb1.5Te3 compounds by ingot extrusion

Abstract p-Type Bi 0.5 Sb 1.5 Te 3 compounds were fabricated by ingot extrusion in the temperature range of 340–460°C. A noble ingot extrusion process was developed for the production of Bi 2 Te 3 -based thermoelectric materials with a high strength and figure of merit. The figure of merit Z increased with extrusion temperature. We obtained the highest figure of merit (Z = 2.70 × 10 −3 /K) at 460°C. The experimental results show that this ingot extrusion is a useful technique for the preparation of good Bi 0.5 Sb 1.5 Te 3 compounds.

Thermoelectric properties of hot-pressed n-type Bi2Te2.85Se0.15 compounds doped with SbI3

The n-type 0.1 wt.% SbI3-doped Bi2Te2.85 compounds were fabricated by hot pressing in the temperature range 380–420°C under 200 MPa in Ar. The density of the compounds was increased to 99.2% of theoretical density. The grains were preferentially oriented through hot pressing. As the pressing temperature was increased, the density and degree of preferred orientation of grains were increased, thus giving rise to an increase in the figure of merit. The figure of merit hot pressed at 420°C was 2.35×10−3/K.

Fabrication and thermoelectric properties of n-type SbI3-doped Bi2Te2.85Se0.15 compounds by hot extrusion

The n-type 0.1 wt% SbI3-doped Bi2Te2.85Se0.15 compounds were fabricated by hot extrusion in the temperature range 300–510°C under an extrusion ratio of 20:1. The extruded compounds were highly dense. The grains were small, equiaxed (∼1.0 μm), and contained many dislocations due to the dynamic recrystallization during the extrusion. The grains were also preferentially oriented through the extrusion. The bending strength and the Fig. 1 of merit of the compounds, hot-extruded at 440°C, were 97 MPa and 2.62 × 10−3/K, respectively.

Effect of extrusion temperature and dopant on thermoelectric properties for hot-extruded p-type Te-doped Bi0.5Sb1.5Te3 and n-type SbI3-doped Bi2Te2.85Se0.15

Abstract The p-type Te-doped Bi 0.5 Sb 1.5 Te 3 and n-type SbI 3 -doped Bi 2 Te 2.85 Se 0.15 compounds were fabricated by hot extrusion in the temperature range of 300–440°C under an extrusion ratio of 20:1. The grains of the two compounds contained many dislocations and were fine equiaxed (∼1.0 μm) owing to the dynamic recrystallization during the extrusion. The hot extrusion gave rise to a slightly preferred orientation of grains. The bending strength and the figure of merit of the two compounds increased with increasing the extrusion temperature. In addition, the Te and SbI 3 dopants significantly increased the figure of merit. The values of the figure of merit for the p-type 4.0 wt.% Te-doped Bi 0.5 Sb 1.5 Te 3 and n-type 0.05 wt.% SbI 3 -doped Bi 2 Te 2.85 Se 0.15 compounds hot extruded at 440°C were 2.94×10 −3 and 3.05×10 −3 K, respectively.

Characteristics of p-type Bi0.5Sb1.5Te3 compounds doped with Te

p-type Bi0.5Sb1.5Te3 compounds doped with 4.0 wt% Te were fabricated by hot pressing in the temperature range 380 to 420°C under 200 MPa in Ar. X-ray diffraction and transmission electron microscopy were used to examine the microstructure. The microstructure was relatively dense and the grains were oriented through the hot pressing. With increasing pressing temperature, both the density and the degree of preferred orientation of grains increased, resulting in an improvement in the figure of merit. The values of the figure of merit obtained along the directions perpendicular to and parallel to the pressing direction for the compounds hot pressed at 420°C were 2.69×10−3 K−1 and 1.92×10−3 K−1, respectively.

Microstructural and Thermoelectric Properties of P-Type Te–Doped Bi 0.5 Sb 1.5 Te 3 And N-Type SbI 3 -Doped Bi 2 Te 2.85 Se 0.15 Compounds

The p-type Te-doped Bi 0.5 Sb 1.5 Te 3 and n-type SbI 3 -doped Bi 2 Te 2.85 Se 0.15 thermoelectric compounds were fabricated by hot pressing in the temperature range of 380 to 440 °C under 200 MPa in Ar. Both the compounds were highly dense and showed high crystalline quality. The grains of the compounds were preferentially oriented and contained many dislocations through the hot pressing. The fracture path followed the transgranular cleavage planes, which are perpendicular to the c-axis. In addition, with increasing the pressing temperature, the figure of merit was increased. The highest values of figure of merit for the p- and n-type compounds, which were obtained at 420 °C, were 2.69 × 10 −3 /K and 2.35×10 −3 /K, respectively.

Microstructure, Mechanical Properties, and Thermoelectric Properties of Hot-Extruded P-Type Te-Doped Bi 0.5 Sb 1.5 Te 3 Compounds

The p-type Bi{sub 0.5}Sb{sub 1.5}Te{sub 3} compounds with Te dopant (4.0 and 6.0 wt%) and without dopant were fabricated by hot extrusion in the temperature range of 300 to 510 C under an extrusion ratio of 20:1. The undoped and Te doped compounds were highly dense and showed high crystalline quality. The grains contained many dislocations and were fine equiaxed ({approximately}1.0 {micro}m) owing to the dynamic recrystallization during the extrusion. The hot extrusion gave rise to the preferred orientation of grains. The bending strength and the figure of merit of the undoped and Te doped compounds were increased with increasing the extrusion temperature. The Te dopant significantly increased the figure of merit. The values of the figure of merit of the undoped and 4.0 wt% Te-doped compounds hot extruded at 440 C were 2.11 x 10{sup {minus}3}/K and 2.94 x 10{sup {minus}3}/K, respectively.

Effect of extrusion process on the thermoelectric properties of hot-extruded n-type Bi/sub 2/Te/sub 2.85/Se/sub 0.15/ compounds

The n-type Bi/sub 2/Te/sub 2.85/Se/sub 0.15/ compounds were fabricated by the hot extrusion under in the temperature range of 300 to 440/spl deg/C under an extrusion ratio of 20:1. The microstructure and thermoelectric properties of the compounds were studied. It was found that the compounds was highly dense. The density was increased with increasing temperature. Also, equiaxed fine grains (/spl sim/1.0 /spl mu/m) were formed because dynamic recrystallization occurred during the extrusion. The hot extrusion gave rise to a slightly preferred orientation of grains. The small grain size and preferred orientation of grains and the high density contributed to an improvement in the thermoelectric properties. The highest figure of merit (2.62/spl times/10/sup -3//K) was obtained at 440/spl deg/C. In addition, the Sbl/sub 3/ dopants significantly increased the figure of merit. The values of the figure of merit for 0.05 wt% Sbl/sub 3/-doped Bi/sub 2/Te/sub 0.85/Se/sub 0.15/ compounds hot extruded at 440/spl deg/C was 3.05/spl times/10/sup -3//K.