Thermoelectric performance enhancement in n-type Bi2(TeSe)3 alloys owing to nanoscale inhomogeneity combined with a spark plasma-textured microstructure

Yu Pan,Jing-Feng Li

doi:10.1038/am.2016.67

Abstract

Bi2Te3 is a good thermoelectric compound that can be adjusted to p- or n-type with corresponding substitutions; however, less progress has been achieved for the property enhancement of n-type Bi2(TeSe)3 compared with p-type (BiSb)2Te3. Textured n-type Bi2(TeSe)3 with an enhanced thermoelectric performance has been developed in this study by combining texturing with in situ nanostructuring effects. The spark plasma-textured structure boosts the electrical transport properties and the power factors as benefits of the layered microstructure. It also leads to a simultaneous rise in the thermal conductivity along the a-axis. We developed a method to suppress increases in the thermal conductivity by inducing nanostructures, such as highly distorted regions and nanoscopic defect clusters, as well as dislocation loops that can form when texturing occurs at an optimized temperature. In this work, textured n-type Bi2(TeSe)3 materials having enhanced thermoelectric performances within a low temperature range are developed with a maximum dimensionless figure of merit (ZTmax) exceeding 1.1 at 473 K. The present method, which synergetically utilizes the texturing and nanostructuring effects, could also be applied to other thermoelectric compounds having layered structures. Materials that convert temperature differences into electricity can gain efficiency with a technique incorporating nondots into textures. Thermoelectric materials based on bismuth telluride are used industrially for electronic cooling and capable of capturing waste heat. Recent findings suggest that these alloys have enhanced capabilities when formed from powders rather than traditional solid ingots. Jing-Feng Li from Tsinghua University in China and colleagues found that spark plasma sintering, which uses short current pulses to solidify powders, forged intriguing textures, defect clusters and dislocation loops into a bismuth–telluride –selenide alloy. Thermoelectric measurements and imaging techniques revealed that the plasma-induced texture boosted electrical transport, while the distorted defects helped trap heat. By tuning the temperature to optimize the ratio of textures to defects, the team raised the thermoelectric figure of merit by 35% compared to non-textured samples. Performance enhancement of n-type Bi2(TeSe)3 is achieved by a combination of spark plasma texturing and nanostructuring techniques, which boost electrical transport properties and suppress a simultaneous increase in thermal conductivity, respectively. A maximum ZT value over 1.1 is obtained in textured n-type Bi2Te2.2Se0.8 bulks, corresponding to 35% enhancement compared with the non-textured counterparts.

Highlights

A bottleneck has existed for the enhancement of n-type Bi2(TeSe)[3] alloys, and high ZTs exceeding 1.0 have been seldom reported in powder-processed n-type Bi2(TeSe)[3] despite higher ZT values demonstrated for p-type (BiSb)2Te3 alloys.[19]
We have demonstrated that a large quantity of nanoscopic defects inside the grains form at an optimized texturing temperature, decreasing the lattice thermal conductivity; a textured structure greatly enhances the electrical transport properties
The textured samples displayed an enhanced intensity of the (00l) peak and weakened intensities of the (110) and (015) peaks compared with the non-textured sample, indicating a preferred orientation along (00l)

Summary

Introduction

A bottleneck has existed for the enhancement of n-type Bi2(TeSe)[3] alloys, and high ZTs exceeding 1.0 have been seldom reported in powder-processed n-type Bi2(TeSe)[3] despite higher ZT values demonstrated for p-type (BiSb)2Te3 alloys.[19] We have demonstrated that a large quantity of nanoscopic defects inside the grains form at an optimized texturing temperature, decreasing the lattice thermal conductivity; a textured structure greatly enhances the electrical transport properties. For the samples textured by repeated SPS, the grains clearly lengthened along the direction normal to the applied pressure, as depicted in Figures 2b–d, which was caused mainly by a crystalline plasticity slip, grain boundary sliding, grain rotation and dynamic recrystallization.[29] the shape of the layered structure was enhanced with increasing texturing temperature.

Results

Conclusion