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Charge Transport Analysis Using the Seebeck Coefficient-Conductivity Relation

Citation

Kang, Stephen Dongmin (2018) Charge Transport Analysis Using the Seebeck Coefficient-Conductivity Relation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ZAQP-MN67. http://resolver.caltech.edu/CaltechTHESIS:05292018-140812451

Abstract

Charge transport properties like electrical conductivity or the Seebeck coefficient are defined phenomenologically from near-equilibrium thermodynamics, while the analysis or modeling of them often involves a physical model based on mechanistic principles. In other words, physical models connect microscopic and physical parameters to phenomenological and experimental properties. One of the challenges is that the complexity of solid state requires many physical parameters, whereas the measurable properties which help to determine those parameters are limited. The interrelations of measured properties are very important to overcome this challenge, but this aspect is not well recognized in conventional analysis themes. In this thesis, the concept of using a phenomenological transport function is devised to help combine a collection of measurements into an intermediate level of phenomenology, relevant for Fermion transport but not dependent on a particular physical model. This phenomenological transport function can be determined by examining the electrical conductivity, the Seebeck coefficient, and potentially the Lorenz number. Because the phenomenological transport function combines information from a set of multiple measurable properties, a direct comparison to the transport function of a physical model serves as a strong test for the model.

Particular usefulness comes from extracting transport functions from the Seebeck coefficient-conductivity relation, especially in doped semiconductors. This approach is applied to contrast CeO2-x and n-type SrTiO3 as narrow and dispersive transport function materials, each consistent with polaron and band conduction, respectively. In band conductors such as SrTiO3 and Mg3Sb2, the approach is used to test and refute previous claims about the scattering mechanism and find consistency with deformation potential scattering in both cases. In conducting polymers, which do not resemble any other type of conventional conductors, the Seebeck-conductivity relation reveals a qualitative disagreement with the commonly cited Mott's models. For the case of Cu2Se, a peculiar band conductor which shows anomalies in the Hall measurement of the high temperature phase and also in other transport properties at the phase transition, the transport function approach is applied as a workaround for modeling. On the practical side, for thermoelectric applications, the transport function approach is used to characterize material quality factors for both majority carrier conduction and bipolar conduction. Finally, experimental efforts for improving the accuracy and applicability of Seebeck measurements is discussed.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Charge Transport; Seebeck coefficient; Thermopower; Conductivity
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Materials Science
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Snyder, G. Jeffrey
Thesis Committee:
  • Faber, Katherine T. (chair)
  • Minnich, Austin J.
  • Bernardi, Marco
  • Snyder, G. Jeffrey
Defense Date:14 May 2018
Non-Caltech Author Email:stephen.d.kang (AT) gmail.com
Record Number:CaltechTHESIS:05292018-140812451
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:05292018-140812451
DOI:10.7907/ZAQP-MN67
ORCID:
AuthorORCID
Kang, Stephen Dongmin0000-0002-7491-7933
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10961
Collection:CaltechTHESIS
Deposited By: Stephen Kang
Deposited On:01 Jun 2018 17:59
Last Modified:08 Jun 2018 22:58

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