Thermoelectric Properties of Texture-Controlled Bi_1.9Sb_0.1Te_2.7Se_0.3 Compounds Prepared by Angular Extrusion Technique

抄録

N-type Bi_1.9Sb_0.1Te_2.7Se_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 μm 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 3.09×10⁻³ K⁻¹ 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.