dc.contributor.author | Rudderham, Cameron | |
dc.date.accessioned | 2019-12-16T16:44:03Z | |
dc.date.available | 2019-12-16T16:44:03Z | |
dc.date.issued | 2019-12-16T16:44:03Z | |
dc.identifier.uri | http://hdl.handle.net/10222/76812 | |
dc.description.abstract | Within the linear response regime, calculation of a material’s thermoelectric transport
parameters requires detailed knowledge of both the electronic band structure and the
electronic scattering rates. While it is possible to calculate both from first-principles
using density-functional theory, rigorous scattering rate calculations can be orders
of magnitude more intensive than band structure calculations, and so in practice
it is common to make use of a simplified scattering model instead. The two most
common such scattering models are the constant-mean-free-path model, the constant-relaxation-
time model. However, recent studies in which the electronic scattering
rates have been rigorously calculated have motivated the use of a third scattering
approximation known as the DOS-scattering model, wherein the electronic scattering
rates are assumed to have the same energy dependence as the density-of-states. While
the latter approximation is believed to be the most physical of the three, it is also the
least commonly used, despite being no more difficult to implement. The overall goal of
this thesis is to understand the extent to which the predictions of the more commonly
used scattering approximations differ from those of the more physical DOS-scattering
model when applied to different classes of electronic band structure.
This work begins by comparing the predictions of these scattering models when applied
to common analytic models of electronic dispersion. It is found that these models
can differ significantly in their predictions, and can even disagree about whether a
particular electronic dispersion feature should improve or degrade performance. In
particular, we find that in the case of the so-called quartic-band model (a simple
analytic model commonly used to describe warped bands), DOS scattering predicts
the existence of a second local maximum in the thermoelectric power factor, a feature
completely missed by both the constant-mean-free-path and constant-relaxation-time
approximations. Motivated by these findings, we use first-principles calculations
of electronic structure to investigate the thermoelectric properties of 2D quintuple-layered
systems of Bi2Te3, Bi2Se3 and Sb2Te3 using the DOS scattering approximation.
These materials display warped band structures qualitatively similar to those
described by the quartic-band model, but have to date only been studied using the
MFP and TAU approximations. To assist with the interpretation of our results, we
introduce a new analytic model of electronic dispersion that qualitatively captures
the main features of the band structures of these materials. It is found that while the
presence of ring-like critical surfaces in the electronic dispersion can lead to excellent
thermoelectric performance, such benefits are highly sensitive to the anisotropy and
energetic alignment of these features. Our findings suggest that these quintuple-layer
systems may be even better thermoelectrics than was previously believed, and suggests
the possibility of a new approach for designing band structures that lead to
highly efficient thermoelectric conversion. | en_US |
dc.language.iso | en | en_US |
dc.subject | Thermoelectrics | en_US |
dc.subject | Two-dimensional materials | en_US |
dc.subject | Density functional theory | en_US |
dc.subject | Analytic dispersion models | en_US |
dc.title | On the thermoelectric efficiency of warped electronic band structures: A comparison of the predictions of common scattering approximations | en_US |
dc.date.defence | 2019-12-06 | |
dc.contributor.department | Department of Physics & Atmospheric Science | en_US |
dc.contributor.degree | Master of Science | en_US |
dc.contributor.external-examiner | n/a | en_US |
dc.contributor.graduate-coordinator | Laurent Kreplak | en_US |
dc.contributor.thesis-reader | Josef Zwanziger | en_US |
dc.contributor.thesis-reader | Theodore Monchesky | en_US |
dc.contributor.thesis-supervisor | Jesse Maassen | en_US |
dc.contributor.ethics-approval | Not Applicable | en_US |
dc.contributor.manuscripts | Not Applicable | en_US |
dc.contributor.copyright-release | Not Applicable | en_US |