Structural, thermal, electrical and mechanical characterizatio of BixSb2-xTe3 nanostructured bulk thermoelectric material

  • Guang Li

Student thesis: Master's Thesis

Abstract

Thermoelectric (TE) phenomena, which involve the conversion between thermal and electrical energy, are expected to play an increasingly important role in meeting the global energy challenge. However, to successfully apply TE devices for commercial use, the efficiency of TE materials need much improvement. The recent development of a random nanostructured bulk TE material has greatly increased the efficiency. Moreover the fabrication of this material is relatively simple and relatively inexpensive. However, to further improve the performance of TE devices based on these materials, great effort needs to be put to better understand thermal and electrical transport and mechanical properties. Such understanding will provide guidance for optimizing fabrication and processing techniques that lead to further improvement on the efficiency of TE devices. In this thesis, various powerful characterization techniques are utilized and improved to study the nanostructured bulk TE material BixSb2-xTe3. Scanning electron microscope (SEM) and transmission electron microscope (TEM) are employed to investigate the microstructure of the sample fabricated by ball milling and hot pressing. Both micron- and nano- sized grains are observed in addition to large amount of nano-precipitates present in the sample. Thermal transport properties are characterized using a pump-probe setup and the thermal conductivity recorded is as low as about 1.0 W/mK at room temperature. Electrical properties are studied by atomic force microscopy with a conductive probe, i.e., conductive atomic force microscope (C-AFM). Furthermore, to enable quantified measurement of material properties by C-AFM, a simple method to calibrate the tip radius in situ is proposed. The reported figure of merit ZT for the studied nanostructured bulk BixSb2-xTe3 alloy is 1.4~1.5. This is a large enhancement compared to the commercially available bulk TE materials which have ZT of ~1.0. Although a high ZT is important to yield high efficiency, it is not enough for the material to serve well in real application condition where the cyclic temperature gradient and inhomogeneous thermal expansion that may occur will cause structural damage and consequently performance degradation. In this study, the mechanical properties of the nanostructured bulk BixSb2-xTe3 are characterized by means of nanoindentation and the results are correlated with microstructure.
Date of Award2012
Original languageAmerican English
SupervisorMatteo Chiesa (Supervisor)

Keywords

  • Thermoelectric materials
  • Nanostructured materials.

Cite this

'