Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Physics

Major Professor

Lilia M. Woods, Ph.D.

Committee Member

Sarath Witanachchi, Ph.D.

Committee Member

Ivan Oleynik, Ph.D.

Committee Member

Razvan Teodorescu, Ph.D.

Keywords

density functional theory, high-throughput, metamaterial, quaternary materials, thermoelectricity, transformation optics

Abstract

The amount of annual energy consumption in today's human world is on an unprecedented level, as most of the energy used for industrial, transportation, and residential purposes are rejected or dissipated as waste heat, it is of crucial importance to find a way to harvest this wasted heat energy and convert it back into usages. Thermoelectric (TE) devices can help to achieve this purpose by utilizing the principle of thermoelectricity such as the Seebeck effect to generate the electric energy from the waste heat. The main challenges are to find TE materials that are highly efficient in energy conversion, low cost and environmental friendly, these goals are not easy to achieve and researchers have spent decades trying to find optimized TE materials that are commercially feasible for large scale applications.

The present thesis is an investigation of the properties of TE materials from both a nano or micro-scale point of view, and TE transport from a macro-scale point of view. The former one consists of the studies of some newly synthesized quaternary materials such as CuZn\textsubscript{2}InTe\textsubscript{4} and AgZn\textsubscript{2}InTe\textsubscript{4}, the earthly abundance and non-toxic nature make these materials promising candidates for TE applications. By using density functional theory (DFT) simulation, the electric and thermal transport properties of these materials are obtained and thus their TE performances can be accessed and compared to the experiment results. Beyond these materials, by using a systematic "cross-substitution" method, we generated a large class of I-II\textsubscript{2}-III-VI\textsubscript{4} quaternary materials starting from II-VI binary compounds, still use DFT simulations, the TE properties of these quaternary materials are obtained, the results can be useful in helping the future experimentalists to study these materials in a systematic manner.

The other point of view is to study the macroscopic TE transport phenomena using the concept and design of metamaterials. One topic we studied is to use the transformation optics (TO) technique to manipulate the TE flow in a pre-designed manner. TO technique is a way to transform the governing equation of certain physical processes with the equations being form-invariant, thus some special effects such as cloaking and concentrating of waves or flows can be achieved. This method is applied to TE phenomena in the present research, and both the theoretical and practical design of the TE cloak, concentrator, rotator, and diffuser are obtained. Another topic we investigated is the decoupling of thermal and electric flows to a certain extent, by arranging the TE composites in parallelly and series connected manner, the effective thermal and electric conductivity will process different dominant directions, thus the thermal and electric flows will prefer different directions, then a separation effect can be achieved.

The goal of the present research is to contribute some more knowledge to the field of TE research by investigating a new class of TE quaternary materials from first-pinciple study, and by proposing a class of metamaterial designs that can achieve various types of TE transport control.

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