Fabrication of Bi₂Te_2.5Se_0.5 by Combining Oxide-reduction and Compressive-forming Process and Its Thermoelectric Properties

산화물환원과 압축성형 공정에 의한 Bi₂Te_2.5Se_0.5 화합물의 제조와 열전특성

We report the effect of plastic deformation on the thermoelectric properties of n-type Bi₂Te_2.5Se_0.5 compounds. N-type Bi₂Te_2.5Se_0.5 powders are synthesized by an oxide-reduction process and consolidated via spark-plasma sintering. To explore the effect of plastic deformation on the thermoelectric properties, the sintered bodies are subjected to uniaxial pressure to induce a controlled amount of compressive strains (-0.2, -0.3, and -0.4). The shaping temperature is set using a thermochemical analyzer, and the plastic deformation effect is assessed without altering the material composition through differential scanning calorimetry. This strategy is crucial because the conventional hot-forging process can often lead to alterations in material composition due to the high volatility of chalcogen elements. With increasing compressive strain, the (00l) planes become aligned in the direction perpendicular to the pressure axis. Furthermore, an increase in the carrier concentration is observed upon compressive plastic deformation, i.e., the donor-like effect of the plastic deformation in n-type Bi₂Te_2.5Se_0.5 compounds. Owing to the increased electrical conductivity through the preferred orientation and the donor-like effect, an improved ZT is achieved in n-type Bi₂Te_2.5Se_0.5 through the compressive-forming process.