Date of Graduation

2017

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Terence Musho

Committee Co-Chair

David Mebane

Committee Member

Aldo Romero

Committee Member

Nithi T Sivaneri

Committee Member

Xueyan Song

Committee Member

Nianqiang Wu

Abstract

Tougher sanctions on fossil fuel emissions and greater energy demand around the globe is forcing us to rely more on renewable energy resources. Clean energy technologies like thermoelectric power generation provides one solution to ease our dependence on non-renewable energy resources. Thermoelectric materials have the capability of directly converting heat to electricity. However, the efficiency of thermoelectrics has been limited due to the inherent coupling of the electronic and thermal carriers. More recently, an avenue to decouple these interactions has been experimental demonstrated using temperature gradient induced spin currents. With this new discovery comes the need for new transport models to understand and optimize their response. In providing a solution, this thesis is focused on the both the development of a 1D spin-transport model and the exploration of a spinel oxide design space comprising Co 3O4, Co2NiO4 and Co2ZnO 4 as the end configurations.;Ferromagnetic cobalt-based spinel oxides are potential candidates for spin-based thermoelectric energy conversion. Substitution of Co+2 and Co+3 ions with other transitional metal cations that exhibit +2 or +3 oxidation states, like Ni and Zn, can affect the net spin-polarization and electronic conductivity of the material. First principles calculations using density functional theory (DFT) were performed on supercells of cobalt-based spinel oxides to obtain their electronic band structure and density of states. The band gap, electron effective mass, the Fermi energy level, and the magnetization of the material configuration were used to calculated its spin transport characteristics in the presence of a temperature gradient.;A spin driven transport model was developed that is based on a non-equilibrium Greens function (NEGF) approach. This model treats both spin channels independently and calculates electronic and spin conductivities, and spin-Seebeck coefficient of the material. The overall thermoelectric figure of merit, ZT, of the material increased when doped Ni and Zn. These trends identified a focus region around Co2.25Ni0.25Zn0.5O4 that has the potential for a huge spin-Seebeck enhancement.

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