Thermoelectric devices convert between temperature gradients and electricity, implying numerous applications, such as powering exploratory space vehicles, industrial waste-heat recovery, and solid- state refrigeration. Thermoelectric devices consist of doped p-type and n-type semiconductor legs, and the overall device efficiency depends on the transport properties of these semiconductor materials. High-performing thermoelectric materials require a high Seebeck coefficient and high electrical conductivity, but these can be conflicting requirements—increasing the doping level increases the electrical conductivity but decreases the Seebeck coefficient. However, electronic band engineering in k-space, or reciprocal space, can partially decouple these properties and yield materials that have a high Seebeck coefficient and electrical conductivity. Specifically, it is beneficial to engineer bands that have complex Fermi surfaces, characterized by high valley (band) degeneracy, carrier pocket anisotropy, and/or low-dimensional transport. The goal of this dissertation is to understand the chemical origins of complex Fermi surfaces by studying the k-dependence of atomic-orbital interactions in various thermoelectric semiconductors. The motivation behind this work is to use this understanding of complex electronic structures to predict chemical trends in band structure behavior, and therefore, predict alloying design strategies for engineering better thermoelectric materials. In this thesis, the tight-binding method, also known as the Linear Combination of Atomic Orbitals, is used in conjunction with density-functional theory, to gain chemical insights into the origins of complex electronic structures in a variety of technologically-relevant thermoelectric material systems, including IV-VI semiconductors, transition-metal-based half-Heusler semiconductors, and Zintl-phase Mg3Sb2.

Creator

• Brod, Madison K

DOI

• https://doi.org/10.21985/n2-arre-q135

Subject

• Materials Science

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16437
• etdadmin_upload_967109

Keyword

• band engineering
• electronic structure
• density functional theory
• thermoelectrics
• group theory
• tight-binding

Date created

• 2023-01-01

Resource type

• Dissertation

Rights statement

• In Copyright