Study On The Synthesis, Characterization And Thermoelectric Property Of Te And Its Compounds

Thermoelectric material is a new kind of functional material, which can realize direct conversionbetween heat and electricity by means of the movement of solid internal carrier. Its extensive applicationprospect in the field of energy and environment makes it a highly competitive alternative energy. But thelow figure of merit （ZT value） of commercial thermoelectric material becomes a key factor constraining itsapplication. Consequently, the most pressing problem is how to increase the figure of merit. As is known tous all, once thermoelectric material nanocrystallized, its thermal conductivity is decreased more markedlythan conductivity, leading to a significant Seebeck coefficient, moreover, its morphological changes mayhighly improve its thermoelectric properties. Furthermore, among all the thermoelectric materials, Te aswell as its compounds were studied earlier and developed more mature. Hence, Te and its compounds werechosen in our study. Many kinds of samples with different morphologies were synthesized by controlledgrowth, their growth mechanism as well as thermoelectric properties were systematically studied at thesame time. The main findings are described as follows:1. We developed a convenient Lewis acid/base-assisted solvothermal method successfully completedthe controlled synthesis of multi-morphology Te crystals. The morphological transformation fromone-dimension （1D） nanorods and nanowires to2D hierarchical flowerlike microarchitecture has beenobserved. Lewis acids/bases were found to be crucial for the formation of the products by not only acting asthe pH regulator but also as the shape controller, owing to their hydrolysis in the solvent to in situ formH⁺/OH-and hydrates. The thermoelectric （TE） papameters of the bulk discs fabricated by dc hot press withthe as-prepared Te NWs were investigated in a temperature range of275-675K. Findings reveal that theas-prepared Te NWs possess a huge Seebeck coefficient （S）, which arrives up to80mVK-1, more than2orders of magnitude higher than Bi₂Te₃, one of the best TE materials. Here we attribute the exceptionallyhigh S of the as-prepared Te NWs to the following factors:（1） quantum confinement effects in Te NWscaused by their structure ballistic TeO₂quantum point contacts （QPCs）;（2） increased local density of statesnear the Fermi energy level in Te NWs.2. On the basis of the above research results, we accomplished that the controlled growth of Teparticles with distinctive morphologies, including flower-like, ball-flowers, nest-like, and sheet-like structures. These structures, self-assembled from nanorods and nanosheets, are systematically studied byadjusting the reaction parameters, such as the amount of NaOH, the volume ratio of EG/EN, the amount ofPVP, and reaction time. Results reveal that the morphology of Te microstructures can be easily controlledby simply altering the reaction conditions and that NaOH plays a crucial role in the final morphology of Teproducts. The growth mechanisms and morphology control of hierarchical Te microstructures are proposedand discussed.3. We successfully prepared monodispersed ZnTe microspheres via a facile, effective and reproducibleone-pot solvothermal process devoid of any solid templates. In the meantime, the reaction conditionsinfluencing the synthesis of these ZnTe microspheres are investigated, such as the zinc source and reactiontime, in which the mechanism of formation of the microspheres was discussed.