Liquid‐Phase Hot Deformation to Enhance Thermoelectric Performance of n‐type Bismuth‐Telluride‐Based Solid Solutions

Abstract

Bismuth‐telluride‐based solid solutions are the best commercial thermoelectric materials near room temperature. For their n‐type polycrystalline compounds, the maximum figures of merit (zTs) are often less than 1.0 due to the degraded carrier mobility resulting from the loss of texture. Herein, a liquid‐phase hot deformation procedure, during which the Bi2(Te,Se)3 ingots are directly hot deformed with the extrusion of liquid eutectic phase, is performed to enhance the thermoelectric performance of n‐type Bi2(Te,Se)3 alloys. The deformation‐induced dynamic recrystallization is remarkably suppressed due to the reduction of nucleation sites and the release of deformation stress by liquid phase, contributing to a weakened carrier scattering and enhanced carrier mobility. The liquid eutectic phase also facilitates the rotation of grains and enhanced (000l) texture, further improving carrier mobility. In addition, the dense dislocations and lattice distortion introduced into the matrix reduce the lattice thermal conductivity. As a result, a high zT value of 1.1 at 400 K is obtained, about 75% increment over the normal one‐step hot deformed alloys. This work not only demonstrates a simple and efficient technique for achieving superior n‐type Bi2Te3‐based materials, but also elucidates the important role of liquid eutectic phase in hot deformation.

Boosted carrier mobility and enhanced thermoelectric properties of polycrystalline Na0.03Sn0.97Se by liquid-phase hot deformation

“…† These emerged phonon scattering centers during the LPHD process may strengthen the phonon scattering and decrease the k l . Additionally, similar to many previous LPS results of Bi 2 Te 3 and SnSe, 42,43,52 excess Te addition led to a slightly increased k l in the Na 0.03 Sn 0.97 Se-x%Te samples, which needs further investigation in the future. Fig.…”

“…It may be a result of the suppression of bipolar effect with improved carrier concentration. 43,52 As shown in Fig. 3d, the LPHD samples exhibited a much higher PF (a 2 s) than the LPS one due to the significantly increased electrical conductivity.…”

“…43,[49][50][51] Recently, the liquid-phase hot deformation (LPHD) technique was proposed in n-type Bi 2 (Te,Se) 3 alloys. 52 This unconventional process combined the advantages of LPS and HD closely, generating the excellent TE properties. In this work, we used the LPHD method to prepare polycrystalline SnSe-based materials.…”

Electronic quality factor for thermoelectrics

“…x = 0.0024 (1.7 × 10 19 ) Bi 2 Te 3 -based alloys (note that Tl 9 BiTe 6 and MgAgSb seem promising as well). However, existing studies have not fully optimized these materials for use in this important temperature range (8,9,13,14,(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and the lower than predicted experimentally realized peak zT indicates available improvements through a further optimization. Guided by the B E developed in this work (section S3), a high thermoelectric performance in both n-type and p-type materials near room temperature is successfully realized (Fig.…”

Magneto-enhanced electro-thermal conversion performance

“…Bi 2 Te 3 -based alloys are a kind of low-temperature TE materials with best performance in the range of room temperature to 200°C, and possess great potential in commercial applications [14][15][16]. Near room temperature, the ZT values of p-type Bi 2 Te 3 -based materials have reached around 1.4 through various methods [17][18][19], while the ZT values for n-type Bi 2 Te 3 -based alloy have been wandering around 0.7 in the last two decades [15,20,21]. The main reason is that n-type Bi 2 Te 3 -based alloys typically have high carrier concentrations from the donor-like effect during sample preparation [22,23], which lowers α and significantly limits their conversion performance.…”