P-type Bi 0:4 Sb 1:6 Te 3 thermoelectric materials were prepared by an angular extrusion technique with rapidly solidified and stacked foils in a temperature range from 643 K to 838 K. Textures of the angular-extruded specimens were observed by Orientation Imaging Microscopy (OIM). The average grain size was monotonously enlarged from 4.7 to 16.1 mm while increasing the extrusion temperature. The texture of the angularextruded specimens shows that the basal planes are preferably aligned along the extrusion direction. Strong textures were observed in specimens extruded at a temperature range from 683 K to 803 K. The carrier mobility of the extruded specimens depends strongly on both the texture strength and grain size. As the extrusion temperature rises, the bending strength decreases. This change in bending strength is in good agreement with the Hall-Petch relationship. A maximum Z value of 3:33 Â 10 À3 K À1 and bending strength of 80.3 MPa were achieved in a specimen angular-extruded at 773 K. The Z value and the bending strength were sufficiently high compared with conventional hot-extruded or hot-pressed specimens. These results indicate that the angular extrusion technique is effective in improving the thermoelectric and mechanical properties of bismuth-telluride based thermoelectric materials.

N-type Bi 1:9 Sb 0:1 Te 2:7 Se 0:3 compounds were prepared by an angular extrusion technique with rapidly solidified and stacked foils. The extrusion temperature was varied from 653 to 838 K. Thermoelectric properties and the crystal orientation of the compounds were evaluated. The textures of the angular-extruded specimens were observed by Orientation Imaging Microscopy (OIM). The sizes of grains ranged from 4.6 to 16.2 mm in the specimens. The texture in the angular-extruded specimen showed that the basal plane where preferably aligned along the extrusion direction. Strong texture was observed in the specimens extruded at the temperature of 813 K. Electrical resistivity was shown to decrease with an increase in the angular-extrusion temperature. However the dependence of the carrier concentration on the extrusion temperature was small. Our study has shown that the decrease in electrical resistivity is mainly due to the increase of carrier mobility and that the carrier mobility strongly depends on the strength of the texture formed by angular extrusion. The highest Z value of 3:09 Â 10 À3 K À1 was derived from the specimen angular-extruded at 813 K. The present result indicates that the angular extrusion technique is effective in improving thermoelectric properties of bismuth-telluride based compounds.

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