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Thermoelectric Properties of Bismuth Antimony Telluride Alloys

Citation

Kim, Hyun-Sik (2016) Thermoelectric Properties of Bismuth Antimony Telluride Alloys. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9RN35V0. http://resolver.caltech.edu/CaltechTHESIS:05262016-230647147

Abstract

Commonly used ozone-depleting refrigerants in refrigerators will be completely phased out in less than 15 years according to the Montreal Protocol. This imminent challenge can be tackled effectively by replacing the current vapor-compression cooling with environmentally sustainable thermoelectric cooling. P-type (Bi0.25Sb0.75)2Te3 alloys have been intensively studied over the past 50 years for cooling applications because of their high thermoelectric performance near room temperature. However, the electronic origin of the high thermoelectric efficiency of (Bi0.25Sb0.75)2Te3 alloys is often understated or ignored completely. In this thesis, the underlying physics of high electronic performance observed in the particular alloy composition, (Bi2Te3).25–(Sb2Te3).75, is investigated. It was demonstrated with two-band transport calculation that the convergence of bands occurred at (Bi2Te3).25–(Sb2Te3).75. A zT improvement of 17 % was also achieved in zone-levelled (Bi0.25Sb.75)2Te3 crystals by controlling their carrier concentration while using the two-band model as a guide. With the optimum electronic efficiency theoretically calculated and achieved experimentally, the thesis moves on to minimize lattice thermal conductivity of (Bi0.25Sb.75)2Te3 for the maximum zT. A new liquid compaction method was devised to produce dense arrays of dislocations in grain boundaries of nanostructured (Bi0.25Sb.75)2Te3. The grain boundary dislocations were found to be highly effective in scattering phonons and a substantial improvement in zT was possible (zT = 1.86 at 320 K). The understanding of phonon scattering by dislocations was in turn applied to phonon scattering at grain boundaries of polycrystalline materials. By demonstrating that the frequency-dependent dislocation scattering can replace the commonly used frequency-independent boundary scattering by Casimir, this thesis suggests that the grain boundary dislocation scattering may be responsible for the mechanism of phonon scattering at grain boundaries.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Thermoelectric, Bismuth Antimony Telluride, Dislocation, Energy gap, Lorenz number
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Snyder, G. Jeffrey
Thesis Committee:
  • Johnson, William L. (chair)
  • Goddard, William A., III
  • Minnich, Austin J.
  • Snyder, G. Jeffrey
Defense Date:23 May 2016
Record Number:CaltechTHESIS:05262016-230647147
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05262016-230647147
DOI:10.7907/Z9RN35V0
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1063/1.4905922Related ItemArticle: and gap estimation from temperature dependent Seebeck measurement—Deviations from the 2e|S|maxTmax relation
http://dx.doi.org/10.1063/1.4908244Related ItemArticle: Characterization of Lorenz number with Seebeck coefficient measurement
http://dx.doi.org/10.1126/science.aaa4166Related ItemArticle: Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics
http://dx.doi.org/10.1038/NMAT4430Related ItemArticle: Convergence of multi-valley bands as the electronic origin of high thermoelectric performance in CoSb3 skutterudites
http://dx.doi.org/10.1039/c5mh00299kRelated ItemArticle: Dislocation strain as the mechanism of phonon scattering at grain boundaries
ORCID:
AuthorORCID
Kim, Hyun-Sik0000-0001-8934-4042
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9780
Collection:CaltechTHESIS
Deposited By: Hyun Sik Kim
Deposited On:09 Mar 2017 17:23
Last Modified:13 Sep 2017 19:07

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