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Superionic Noble Metal Chalcogenide Thermoelectrics


Day, Tristan William (2015) Superionic Noble Metal Chalcogenide Thermoelectrics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9862DCD.

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Measurements and modeling of Cu2Se, Ag2Se, and Cu2S show that superionic conductors have great potential as thermoelectric materials. Cu2Se and Ag2Se are predicted to reach a zT of 1.2 at room temperature if their carrier concentrations can be reduced, and Cu-vacancy doped Cu2S reaches a maximum zT of 1.7 at 1000 K. Te-doped Ag2Se achieves a zT of 1.2 at 520 K, and could reach a zT of 1.7 if its carrier concentration could be reduced. However, superionic conductors tend to have high carrier concentrations due to the presence of metal defects. The carrier concentration has been found to be difficult to reduce by altering the defect concentration, therefore materials that are underdoped relative to the optimum carrier concentration are easier to optimize. The results of Te-doping of Ag2Se show that reducing the carrier concentration is possible by reducing the maximum Fermi level in the material.

Two new methods for analyzing thermoelectric transport data were developed. The first involves scaling the temperature-dependent transport data according to the temperature dependences expected of a single parabolic band model and using all of the scaled data to perform a single parabolic band analysis, instead of being restricted to using one data point per sample at a fixed temperature. This allows for a more efficient use of the transport data. The second involves scaling only the Seebeck coefficient and electrical conductivity. This allows for an estimate of the quality factor (and therefore the maximum zT in the material) without using Hall effect data, which are not always available due to time and budget constraints and are difficult to obtain in high-resistivity materials. Methods for solving the coherent potential approximation effective medium equations were developed in conjunction with measurements of the resistivity tensor elements of composite materials. This allows the electrical conductivity and mobility of each phase in the composite to be determined from measurements of the bulk. This points out a new method for measuring the pure-phase electrical properties in impure materials, for measuring the electrical properties of unknown phases in composites, and for quantifying the effects of quantum interactions in composites.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:thermoelectrics;semiconductors;effective medium theory;electronic transport;copper selenide;silver selenide;copper sulfide;superionic conductors
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Minor Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Snyder, G. Jeffrey
Thesis Committee:
  • Haile, Sossina M. (chair)
  • Snyder, G. Jeffrey
  • Kornfield, Julia A.
  • Flagan, Richard C.
Defense Date:15 May 2015
Non-Caltech Author Email:tristanwday (AT)
Funding AgencyGrant Number
US Air Force Office of Scientific ResearchUNSPECIFIED
Record Number:CaltechTHESIS:05302015-170849147
Persistent URL:
Related URLs:
URLURL TypeDescription DOIArticle adapted for ch. 5 adapted for ch. 6 adapted for ch. 7
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8946
Deposited By: Tristan Day
Deposited On:02 Jun 2015 18:33
Last Modified:04 Oct 2019 00:08

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