Improving Thermoelectric Performance Through Defect Engineering with an Emphasis on the Mesoscale

Grovogui, Jann Albert

doi:https://doi.org/10.21985/n2-vzky-wg19

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Improving Thermoelectric Performance Through Defect Engineering with an Emphasis on the Mesoscale

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Thermoelectric materials are of particular interest in a variety of fields because of their ability to directly convert heat to electricity (and vice versa), however, they struggle to gain widespread adoption because of their low efficiency. A common strategy in the field of thermoelectricity is to introduce material defects into thermoelectrics from the atomic to the millimeter scale to increase the energy conversion efficiency. This dissertation discusses how the incorporation of electron microscopy, particularly at the mesoscale, was used to study structural defects to formulate processing-structure-property relationships and to develop design principles necessary for the fabrication of high performance bulk chalcogenide thermoelectric materials. Electron Backscattered Diffraction (EBSD) and Energy Dispersive Spectroscopy (EDS) were used in parallel to reveal compositional changes that occur during Spark Plasma Sintering in NaPbmSbTem+2, and subsequent studies of the Se and S analogues helped uncover a grain boundary screening effect that can be used to optimize any material that has a low dielectric constant. Melt-Centrifugation of Bismuth Antimony Telluride (BST) proved the benefits of including microstructural defects across multiple length scales, while Induction Hot Pressing and thermal annealing of BST illustrated that similar microstructures could be introduced in a more controlled fashion. Furthermore, sample swelling during annealing implicated creep as a critical mechanism for property enhancement. Lastly, a fundamental study of extrinsic doping in PbSe emphasized the effect that dopants and microstructure have on the thermal stability of thermoelectric materials and revealed a variety of microstructural-dopant relationships that can be manipulated by controlling specific processing procedures.

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