Improved thermoelectric properties of nanostructured composites out of Bi1−xSbx nanoparticles and carbon phases

Ekrem Güneş,Peter J Klar,Eckhard Müller,Matthias T Elm,Mathias S Wickleder

doi:10.1063/1.5034525

Ekrem Güneş, Peter J Klar + Show 3 more

Open Access

https://doi.org/10.1063/1.5034525

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Abstract

Thermoelectric figures of merit of ZT ≈ 0.4 at room temperature were achieved in nanostructured composite materials prepared by uniaxial pressing of Bi1−xSbx nanoparticles and 0.3 wt.% of a carbon phase. This constitutes a significant improvement of the low-temperature thermoelectric material Bi1−xSbx and strongly suggests the possibility of employing these materials in efficient thermoelectric devices working at room temperature. Interestingly, the beneficial effect of the carbon phase added to nanostructured Bi1−xSbx is the same for either carbon nanotubes or active carbon. This finding is attributed, on the one hand, to a combination of electronic band gap engineering due to nanostructuring and energy filtering due to graphene-like interlayers between Bi1−xSbx grains and, on the other hand, to modified phonon scattering at the grain boundaries and additional phonon scattering by agglomeration sites of carbon material on the μm scale.

Highlights

The growing demand of energy and the society’s awareness of environmental issues such as global warming constitute driving forces for tapping renewable energy sources such as sun light or wind instead of fossil fuels,[1,2] and for improving the efficiency of existing energy conversion processes.[3,4,5] Thermoelectric generators possess the potential of converting an additional fraction of the large amounts of unused waste heat of combustion processes in automobiles, industrial plants, and other facilities into electricity and to diminish these losses
Nanostructured composite materials prepared by compacting mixtures of Bi1−xSbx nanoparticles with carbon phases such as Carbon nanotubes (CNT) or active carbon (AC) possess thermoelectric properties superior to those of the nanostructured Bi1−xSbx reference samples
The experimental data can be consistently explained by the formation of carbon-like layers between the Bi1−xSbx nanoparticles of the composites accompanied by the formation of agglomeration sites of the carbon material on the μm scale

Summary

INTRODUCTION

Are often chosen as one constituent of such hybrid materials due to their unusual mechanical, thermal and electrical properties.[10,18,19,20,21,22,23] We have recently demonstrated that nanostructured composites of CNT and Bi1−xSbx nanoparticles exhibit considerably improved thermoelectric properties.[24] Here, we show that nanostructured composites of active carbon (AC) and Bi1−xSbx nanoparticles exhibit similar thermoelectric properties than the original Bi1−xSbx/CNT composites. These findings implies that the improvement of the thermoelectric properties of Bi1−xSbx/CNT composites is not related to the tubular structure of CNT or a resulting CNT network interpenetrating the nanostructured Bi1−xSbx but rather to carbon-related modifications of the interfaces between the Bi1−xSbx nanoparticles

EXPERIMENTAL DETAILS

Characterization of the microstructure

Characterization of the thermoelectric properties

SUMMARY