(630e) Thermoelectric Properties of Bulk Pellets of Unfunctionalized and Functionalized Zn3P2 Nanowires

Zinc phosphide (Zn₃P₂) nanowire powders, both unfunctionalized and surface-functionalized with organic molecules to passivate the surfaces, were mass produced using reactive vapor transport of phosphorus onto zinc foils in a hot-walled chemical vapor deposition chamber, and hot-pressed into dense pellets for the characterization of their thermoelectric performance. The intent here is to explore the possibility of fabricating thermoelectric modules using inexpensive compound semiconductors. Contrary to expectations, the hot-pressing did not alter the morphology or the dimensions of the nanowires in the pellets, despite the fact that high packing densities (>98%) were achieved in the pellets. It was observed that enhanced flexibility observed in thin nanowires allows for their assembly into highly dense pellets, without any morphological alterations. The elastic nature of the Zn₃P₂ nanowires with diameters less than 50 nm was confirmed using in-situ transmission electron microscopy (TEM) studies.

Overall, this experimentation indicated that a 30% reduction in thermal conductivity relative to the bulk is feasible by synthesizing Zn₃P₂ in nanowire format. At the same time, this procedure did not adversely affect the electrical conductivity. In fact, prevention of surface oxidation by functionalizing the nanowires with 1,4-benzenedithiol before their assembly into pellets led to an overall increase in the electrical conductivity of the nanowire pellets. These measurements indicate that it is possible to enhance the thermoelectric performance of materials by synthesizing them in nanowire format. The thermoelectric performance of both unfunctionalized and functionalized Zn₃P₂ nanowire pellets, along with those obtained using by doping them with copper, will be discussed in detail in this presentation.