Theoretical studies of the thermoelectric properties of nanostructured materials

This project involves theoretical study of the thermoelectric properties of lead chalcogenidematerials. Thermoelectric (TE)materials are used for the fabrication of devices that are designed to convert heat into electricity and vice versa. They can be described as a clean alternative for fossil fuel. These materials are characterized by their ability to operate at a broad range of temperatures (2 − 800) K. Lead chalcogenides, such as PbTe, PbSe, and PbS, represent a group of TE materials that have the appealing property of stability at high temperatures, hence they are considered attractive for thermoelectric applications. The simple rocksalt structure of lead chalcogenide combined with its narrow gap semiconductor’s nature has attracted great attention form experimental as well as theoretical researchers. These studies have focused on investigating electronic structures and elastic properties aiming for a better understanding that would lead to a significant improvement in their TE efficiency. In the first part of this thesis we evaluated the optimised parameters for the figure of merit for n-type PbTe: The electrical conductivity, the Seebeck coefficient, and the total thermal conductivity, (i.e. the electronic and lattice thermal conductivity), emphasising on the important role of optical phonons in heat conduction. In the second part, we extended the lattice thermal conductivity work to include PbSe, PbS, and SnTe, where we applied the Debye, Callaway, and Allen theories of thermal conductivity. In the third part we used the effective medium theory to evaluate the lattice thermal conductivity for PbTe-PbSe nanocomposites in three different configurations: nanospheres, nanowires, and superlattices