Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Manasreh, Bothina H.

Committee Member

Bellaiche, Laurent

Second Committee Member

Churchill, Hugh O.H.

Third Committee Member

Kumar, Pradeep

Keywords

Electronic and Structural Properties; Lattice Anharmonicity; Lattice Dynamics; Lattice Thermal Conductivity; Thermoelectrics

Abstract

The aim of this dissertation is the investigation of thermoelectric and lattice dynamics properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Se, Te) and ZrS2 compounds based on the first-principles density functional theory. The dimensionality reduction (e.g., using 2D structure) of bulk materials is found to have enhanced thermoelectric efficiency. This enhancement is attributed to the increase of the Seebeck coefficient as a result of higher electronic density of states near the Fermi level in low-dimensional materials. In addition, lowering the dimensionality increases phonon scattering near interfaces and surfaces in 2D materials, which leads to a reduction of the lattice thermal conductivity (?!) and consequently to a higher efficiency. Particularly, for the materials used in the present investigation, the low-energy acoustic phonon modes are found to play a major role to the total ?!. Beyond the conventional 0 K harmonic lattice dynamics approach, I performed the finite-temperature and anharmonic lattice dynamics calculations of 2D ZrS2 and SnTe monolayers (MLs) by using a well-tested self-consistent phonon (SCP) theory, which implements compressive sensing lattice dynamics technique based on the efficient machine learning algorithms within it. The inclusion of lattice anharmonicity was found to increase the lattice thermal conductivity due to the increase in the thermodynamic parameters: group velocity, phonon lifetime, and specific heat capacity. In addition, I also studied the structural stability, electronic, and magnetic properties of transition-metal (Mn, Fe, and Co) atoms adsorbed SnX (X = S, Se, and Te) MLs. In these investigations, the antiferromagnetic orderings are realized between these TM and SnX atoms with the highest magnetic moments induced for Co atoms adsorbed SnS and SnTe MLs. The adsorption of these TM atoms is found to reduce the electronic band gaps in comparison to the corresponding pristine SnX MLs.

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