Compositional disorder and its effect on the thermoelectric performance of ZnP nanowire-copper nanoparticle composites.
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Recent studies indicated that nanowire format of materials is ideal for enhancing the thermoelectric performance of materials. Most of these studies were performed using individual nanowires as the test elements. It is not currently clear whether bulk assemblies of nanowires replicate this enhanced thermoelectric performance of individual nanowires. Therefore, it is imperative to understand whether enhanced thermoelectric performance exhibited by individual nanowires can be extended to bulk assemblies of nanowires. It is also imperative to know whether the addition of metal nanoparticle to semiconductor nanowires can be employed for enhancing their thermoelectric performance further. Specifically, it is important to understand the effect of microstructure and composition on the thermoelectric performance on bulk compound semiconductor nanowire-metal nanoparticle composites. In this study, bulk composites composed of mixtures of copper nanoparticles with either unfunctionalized or 1,4-benzenedithiol (BDT) functionalized ZnP nanowires were fabricated and analyzed for their thermoelectric performance. The results indicated that use of BDT functionalized nanowires for the fabrication of composites leads to interface-engineered composites that have uniform composition all across their cross-section. The interface engineering allows for increasing their Seebeck coefficients and electrical conductivities, relative to the ZnP nanowire pellets. In contrast, the use of unfunctionalized ZnP nanowires for the fabrication of composite leads to the formation of composites that are non-uniform in composition across their cross-section. Ultimately, the composites were found to have ZnP nanowires interspersed with metal alloy nanoparticles. Such non-uniform composites exhibited very high electrical conductivities, but slightly lower Seebeck coefficients, relative to ZnP nanowire pellets. These composites were found to show a very high zT of 0.23 at 770 K, orders of magnitude higher than either interface-engineered composites or ZnP nanowire pellets. The results indicate that microstructural composition of semiconductor nanowire-metal nanoparticle composites plays a major role in determining their thermoelectric performance, and such composites exhibit enhanced thermoelectric performance.