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Band Engineering in Thermoelectric Materials Using Optical, Electronic, and Ab-Initio Computed Properties

Citation

Gibbs, Zachary Michael (2015) Band Engineering in Thermoelectric Materials Using Optical, Electronic, and Ab-Initio Computed Properties. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9XS5S9Z. https://resolver.caltech.edu/CaltechTHESIS:05142015-004120562

Abstract

Thermoelectric materials have demanded a significant amount of attention for their ability to convert waste heat directly to electricity with no moving parts. A resurgence in thermoelectrics research has led to significant enhancements in the thermoelectric figure of merit, zT, even for materials that were already well studied. This thesis approaches thermoelectric zT optimization by developing a detailed understanding of the electronic structure using a combination of electronic/thermoelectric properties, optical properties, and ab-initio computed electronic band structures. This is accomplished by applying these techniques to three important classes of thermoelectric materials: IV-VI materials (the lead chalcogenides), Half-Heusler’s (XNiSn where X=Zr, Ti, Hf), and CoSb3 skutterudites.

In the IV-VI materials (PbTe, PbSe, PbS) I present a shifting temperature-dependent optical absorption edge which correlates well to the computed ab-initio molecular dynamics result. Contrary to prior literature that suggests convergence of the primary and secondary bands at 400 K, I suggest a higher convergence temperature of 700, 900, and 1000 K for PbTe, PbSe, and PbS, respectively. This finding can help guide electronic properties modelling by providing a concrete value for the band gap and valence band offset as a function of temperature.

Another important thermoelectric material, ZrNiSn (half-Heusler), is analyzed for both its optical and electronic properties; transport properties indicate a largely different band gap depending on whether the material is doped n-type or p-type. By measuring and reporting the optical band gap value of 0.13 eV, I resolve the discrepancy in the gap calculated from electronic properties (maximum Seebeck and resistivity) by correlating these estimates to the electron-to-hole weighted mobility ratio, A, in narrow gap materials (A is found to be approximately 5.0 in ZrNiSn).

I also show that CoSb3 contains multiple conduction bands that contribute to the thermoelectric properties. These bands are also observed to shift towards each other with temperature, eventually reaching effective convergence for T>500 K. This implies that the electronic structure in CoSb3 is critically important (and possibly engineerable) with regards to its high thermoelectric figure of merit.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Thermoelectrics, band engineering, absorption edge, Seebeck
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Snyder, G. Jeffrey
Thesis Committee:
  • Haile, Sossina M. (chair)
  • Snyder, G. Jeffrey
  • Giapis, Konstantinos P.
  • Minnich, Austin J.
Defense Date:11 May 2015
Non-Caltech Author Email:zachary.m.gibbs (AT) gmail.com
Funders:
Funding AgencyGrant Number
U.S. Dept. of EnergyDE-AC02-05CH11231
Record Number:CaltechTHESIS:05142015-004120562
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:05142015-004120562
DOI:10.7907/Z9XS5S9Z
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1088/1367-2630/15/7/075020DOIBurstein Moss Shift in PbTe
http://dx.doi.org/10.1063/1.4858195DOITemperature Dependent Band Gap in PbTe, PbSe, and PbS
http://dx.doi.org/10.1039/C3EE43438ADOIBand Engineering in Pb1-xSrxSe
http://dx.doi.org/10.1039/C4CP02091JDOIIodine Doping in SnTe
http://dx.doi.org/10.1039/C4MH00142GDOIResolving the true band gap in ZrNiSn
http://dx.doi.org/10.1063/1.4905922DOIBand gap estimation using the maximum Seebeck coefficient and the Goldsmid Sharp method
http://dx.doi.org/10.1039/C5TA01967BDOISr5In2Sb6 Zintl compound
http://dx.doi.org/10.1021/cm300520wDOIZintl 5-2-6 compounds
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8859
Collection:CaltechTHESIS
Deposited By: Zachary Gibbs
Deposited On:27 May 2015 21:40
Last Modified:04 Oct 2019 00:07

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PDF (Full Thesis) - Final Version
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PDF (Chapter 0: Thesis Preinfo and Contents) - Final Version
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PDF (Chapter 1: Introduction) - Final Version
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PDF (Chapter 2: Theoretical and Experimental Methods) - Final Version
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PDF (Chapter 3, Optical Properties of Doped Semiconductors) - Final Version
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PDF (Chapter 4: Multi Band Behavior, Optical, and Electronic Properties in IV-VI materials) - Final Version
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PDF (Chapter 5: Resolving the True Band Gap in ZrNiSn: The Effect of the Weighted Mobility Ratio in Bipolar Semiconductors) - Final Version
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PDF (Chapter 6: CoSb3 and other Thermoelectric Materials with Optical Evidence of Multiple Bands) - Final Version
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PDF (Chapter 7: The “Fermi Surface Complexity Factor” and Band Engineering using Ab-Initio Boltzmann Transport Theory) - Final Version
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PDF (Chapter 8: Conclusions and Future Directions) - Final Version
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