소성변형을 거친 비스무스 텔루라이드 소결체의 열전특성 분석

Abstract

Bismuth telluride (Bi2Te3)-based alloys are widely used for thermoelectric cooling and powergeneration at low temperatures, and they are the only commercially available materials for thermoelectricapplications below 500 K. The rhombohedral unit cell with a large c/a lattice constant ratio consisting of -Te-Bi-Te-Bi-Te- stacked layers inevitably brings about a large anisotropy in transport properties, which is whytexturing is very important in polycrystalline Bi2Te3 alloys for maximum performance. In this report, p andn-type polycrystalline Bi2Te3 alloys were synthesized and hot-deformed to investigate the effects of texturingon thermoelectric properties. Hot deformation (HD) induces the strong alignment of (00l) orientations alongthe compression direction, and a remarkable increase in the orientation factor F of (00l) orientations isobserved after HD in both p and n-type materials. All of the hot-deformed polycrystalline samples showedincreased electrical conductivity (), power factor (PF), and thermal conductivity (κ) in the in-plane (IP)direction, and vice versa in the out-of-plane (OOP) direction, which makes the IP direction of the hot-deformedbodies more favorable for module fabrication in terms of power factor, for both p and n-type Bi2Te3-basedalloys. However, due to the different degree of anisotropy of κ and , the figures of merit (zT) were maximizedin the OOP direction in the p-type materials after HD, whereas the zTs of the n-type materials were higherin the IP direction. This occurs because the anisotropy factor of electron conduction is higher than that of holeconduction, which more than offsets the advantage of the smaller κ in the c-direction of n-type Bi2Te3. Themaximum zT of 1.33 (OOP) and 0.90 (IP) were obtained after HD from the p and n-type Bi2Te3 alloys,respectively, which were 9.3% and 18.4% higher than those of as-sintered materials.