The Influence of Carbon Nanotubes on the Thermoelectric Properties of Bismuth Telluride

Abstract

Thermoelectric materials are devices that have the ability to convert waste heat to electricity. The widespread use of thermoelectric materials is currently limited by the low value of their figure-of-merit (ZT). Bismuth Telluride (Bi2Te3) is a promising thermoelectric material in the near room temperature applications that provides a ZT value ~ 1. In order to overcome the limitation of utilizing thermoelectric materials in waste heat recovery, a ZT value > 2 is required. In this current study, multi-walled carbon nanotubes (MWCNT) were incorporated into the Bi2Te3 bulk matrix system to enhance its mechanical and thermoelectric properties through powder processing techniques. The nanocrystalline Bi2Te3/MWCNT composites were prepared using high energy ball milling and spark plasma sintering (SPS) techniques. The structural characterization and the average grain size values of both pristine Bi2Te3 and Bi2Te3/MWCNT were found to be approximately (~ 13 nm), and the average strain was found to be 0.2 using both X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. Vickers Microhardness test shows significant improvement of the nanocomposite hardness up to ~2 GPa as a function of increasing the MWCNT content. As for the dimensionless figure of merit (ZT) of the composite, it is expected to increase above the value of the pure binary Bi2Te3 in the temperature range of 298–498 K the addition of MWCNT increased the ZT value from 0.48 to maximum ZT value to 0.61 at 50oC, while at 150oC the ZT value was measured to be 0.35 and 0.43 for Bi2Te3 and MWCNT/Bi2Te3, respectively. It is considered that the enhancement of the thermoelectric performance of the composite mostly derived from the thermal conductivity, which is reduced by an active phonon-scattering at the MWCNT/Bi2Te3 interfaces