Transport properties of thermoelectric materials displaying structural phase transition

Developing renewable, sustainable, and environmentally friendly energy conversion technologies is crucial for addressing the global energy crisis. Waste heat recovery using thermoelectric materials has emerged as a promising solution to support energy sustainability. The efficiency of thermoelectric materials depends on their figure of merit, zT, which represents their ability to convert heat into electricity. However, achieving optimal zT values in thermoelectric materials is a complex task due to the interdependence of transport properties. This thesis study focused on phase-changing binary copper chalcogenides (Cu3-xTe2 and Cu2Se) and Li3Sb, as well as a p-type half-Heusler compound, NbCoSn, to investigate their synthesis, characterization, and thermoelectric properties. Synthetic rickardite mineral, Cu3-xTe2 samples exhibited phase transitions, with the second transition leading to improved thermoelectric performance. Zn- and Ag-substitution on the samples affected the phase transition temperature and transport properties. Cu2Se, another thermoelectric material, was studied for its mid-temperature thermoelectric performance. Two synthesis methods were employed, and the incorporation of nano-B or C-coated nano-B was investigated. The study on c-Li3Sb focused on its high-energy ball milling synthesis method and observed stress/pressure-induced phase transitions. The thermoelectric properties of c-Li3Sb showed degenerate semiconducting behavior, but its air sensitivity posed challenges for implementation in energy harvesting applications. Addressing the poor thermoelectric performance of p-type NbCoSn was investigated through Co-deficiency and Zr-substitution. Zr-substitution was found to be more effective in improving the thermoelectric properties of the material.