Graduation Year

2019

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

George S. Nolas, Ph.D.

Committee Member

Ivan I. Oleynik, Ph.D.

Committee Member

Venkat R. Bhethanabotla, Ph.D.

Keywords

bournonites, chalcogenides, clathrates, first principles simulations, thermal conductivity, thermoelectricity

Abstract

Thermoelectric materials play an important role in energy conversion as they represent environmentally safe and solid state devices with a great potential towards enhancing their efficiency. The ability to generate electric power in a reliable way without using non-renewable resources motivates many experimentalists as well as computational physicists to search and design new thermoelectric materials. Several classes of materials have been identified as good candidates for high efficient thermoelectrics because of their inherently low thermal conductivity. The complex study of the crystal and electronic structures of such materials helps to reveal hidden properties and give fundamental understanding, necessary for the development of a new generation of thermoelectrics.

In the current thesis, ab-initio computational methods along with experimental observations are applied to investigate several material classes suitable for thermoelectric applications. One example are Bi-Sb bismuth rich alloys, for which it is shown how structural anomalies affect the electronic structure and how inclusion of the Spin-Orbit coupling is necessary for this type of materials. Another example are bournonite materials whose low thermal conductivity is attributed to distortions and interactions associated with lone-electron s^2 pair distributions. In addition, it is shown how doping with similar atoms can affects electronic structure of these materials leading to changes in their transport properties. Clathrate materials from the less studied type II Sn class are also investigated with a detailed analysis for their structural stability, electronic properties and phonons. These systems are considered with partially substituted atoms on the framework and different guests inside. The effect upon insertion of Noble gases into the cage network is also investigated. In addition, the newly synthesized As based cationic material is also studied finding novel structure-property relations. Another class of materials, quaternary chalcogenides, have also been studied. Because of their inherently low thermal conductivity and semiconducting nature their transport properties may be optimized in a favorable way for thermoelectricity.

The present work provides an in-depth study of structural and electronic properties of several classes of materials, which can be used by experimentalists for input and guidance in the laboratory.

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