Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Microelectronics-Photonics (PhD)

Degree Level

Graduate

Department

Graduate School

Advisor

Bothina Manasreh

Committee Member

Omar Manasreh

Second Committee Member

William Oliver

Third Committee Member

Simon Ang

Fourth Committee Member

Rick Wise

Keywords

Heusler compounds, monochalcogenides, Seebeck coefficient, Spintronics, Thermodynamics, Thermoelectric

Abstract

The electronic, magnetic, and thermoelectric properties of transition-metal based compounds were investigated by using the density functional theory and Boltzmann transport formalism. It was found that the Co-based Heusler compounds and InSe monochalcogenide are among the materials that may be used for future thermoelectric devices. Furthermore, the investigation showed that the quaternary Heusler compounds, such as, CoFeYGe, where Y is Ti or Cr, are half-metallic ferromagnetic materials with full electron spin polarization. The lattice thermal conductivity (κL) was found to decrease for these alloys as the temperature increases. The present investigation indicated that the phonon optical modes have a major contribution to the total κL as compared to the acoustic modes. It was also found that these compounds can be doped as either n- or p-type thermoelectric materials. The n-type material was found to possess higher thermoelectric efficiency as compared to the p-type. The calculations showed different behaviors of CoFeCuZ (Z= Al, As, Ga, In, Pb, Sb, Si, Sn) quaternary Heusler compounds. Two compounds, with Z = Al, As showed a metallic behavior, while the compounds with Z = Ga, In, Sb, Si, and Sn showed a nearly half-metallic behavior. Only CoFeCuPb was found to exhibit a half-metallic ferromagnetic behavior with a full electron spin polarization. The thermoelectric power factor of CoFeCuPb is high at room temperature and increases at higher temperatures. In addition, doping β-InSe with Bi atoms at the Se sites was found to decrease its lattice thermal conductivity, which leads to an increase in its figure of merit.

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