Thermoelectric materials, converting waste heat into electrical energy, are recently recognised as a key class of energy materials worldwide. Nano-scaled thermoelectric materials are predicted to exhibit outstanding thermoelectric performance rather than bulk materials due to the low dimensional quantum size effect. Although current experimental works proved a few promising thermoelectric properties of nanomaterials, more intensive works should be investigated to achieve more improvable properties. Moreover, the thermoelectric nanomaterials can be used as essential building blocks for nano devices which applied in power generation and refrigeration, especially in nano devices.
Nano-scaled tellurium-based materials are targeted in this project and expected to make a breakthrough because that the bulk tellurium-based materials have already been extensively investigated and commercially used in thermoelectric devices with a just acceptable performance, but their enhancement of thermoelectric converting efficiency encounters difficult due to the existence of conflict properties which determine the thermoelectric performance. Therefore, fabricating high quality tellurium-based nanomaterials and further understanding their growth mechanisms and improving their thermoelectric performance is quite challengeable and key to realize real application in power generation and refrigeration.
For synthesizing high-quality tellurium-based nanomaterials, in this Mphil project, solvothermal method has been chosen. A green and facile solvothermal route has been developed to obtain high quality tellurium nanostructures. Tellurium nanowires with unique tri-fold structure were synthesized and their morphologies were modified by applying different experimental parameters. The tri-fold tellurium nanowires were obtained when they chemical reacted in a mixture solvent contented distilled water and ethylene glycol with the existence of PVP as the surfactant. The growth mechanism of tri-fold tellurium nanowires has been investigated based on the characterization using transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and crystal structural simulation. An induced growth of hexagonal tellurium crystal nuclei under high temperatures and pressures is believed as the reason of forming tellurium nanowires with tri-fold symmetric structure.
Furthermore, Lead telluride, one of the materials with the highest thermoelectric performance in the intermediate temperature range, has been successfully fabricated with nanostructures. The lead telluride crystal has different growth mechanism when the lead source was varied. When the solvent was changed from a mixture of ethylene glycol and deionised water to pure ethylene glycol, the obtained lead telluride was changed from tri-fold nanowires to nanorods. In a face-centre-cubic lead telluride crystal, the (111) plane is the strong plane. The characterization of tri-fold lead telluride showed the crystal growth along the  direction, which indicated the thermal dynamic growth of lead telluride based on the tri-fold tellurium template. When the reaction parameters were changed, the lead telluride crystal tended to grow along the  direction in the face-centre-cubic lattice.
Overall, this master of philosophy project aimed to establish the thorough understanding of thermoelectric property and master the synthesizing and characterization methods, furthermore, understand the growth of tellurium-based materials. Based on the investigations, advanced high-quality thermoelectric nanomaterials have been developed and could be used in nano devices for power generation.