The Synthesis, Characterization And Thermoelectric Properties Of Te/TiS₂ Nanocables

Thermoelectric materials are a new kind of functional material, which can realize direct conversion between heat and electricity by means of the movement of solid internal carrier. Their extensive application prospect in the field of energy and environment make them a highly competitive alternative energy. The performance of TE devices is quantized by a figure of merit(ZT), where Z is a measure of a material’s TE properties and T is the absolute temperature. The dimensionless thermoelectric ZT could determine the performance of a TE material, ZT =(S2σ/?)T, where S, σ, ?, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Based on the nanostructuring of thermoelectric material, the thermal conductivity would be reduced more than the electrical conductivity, which can significantly improve the figure of merit. Furthermore, among all the thermoelectric materials, Te as well as its compounds were studied earlier and developed more mature, which has been acknowledged and researched extensively. As is known to us all, developing thermoelectric materials of noval structures is of key scientific significance and practical value for treating pollution and overcoming energy shortage. Among all, nanocable structured thermoelectric material, due to its characteristics one-dimentional nanostructure, as well as a core-shell interface between the two phases of its inner core and the coat diametrical-wise, possesses impressive characters, rich scientific meanings and potential for superior thermoelectric figure of merit. Hence, Te, TiS2 and their compounds were chosen in our study. Many kinds of samples incuding Te nanowires, TiS2 nanowires and Te/TiS2 heterostructure nanocables were synthesized by controlled growth. Their growth mechanism as well as thermoelectric properties were systematically studied at the same time. The main findings are described as follows:1. The product of Te nanostructure were prepared by a simple solvothermal method controlly, whose morphology were one-dimensional nanowires. The thermoelectric(TE) papameters of the individual Te nanowires fabricated by solvent thermal method were investigated in a temperature range of 4-266 K by a four electrode method. Findings reveal that the conductivity of Te nanowire synthesized is almost not affected by the temperature through 200 K to 266 K, of which the highest conductivity is about to 5.0 ? 105 ?-1m-1. What is more, the lowest thermal conductivity is about to 0.50 Wm-1K-1, which is so much low. Its highest seebeck coefficient is about to-121×10- 6 VK– 1。2. In order to synthesize Te/TiS2 heterostructure nanocables successfully, on the basis of the above research results, we found that the controlled growth of TiS2 nanowires and studied their thermoelectric properties. The products of TiS2 nanostructure were prepared by a simple physical vapor deposition(PVD) growth process controlly, whose morphology were one-dimensional nanowires. The results show that the conductivity of obtained TiS2 nanowire is about to two orders of magnitude lower than the Te nanowires. What is more, the lowest thermal conductivity is about to 0.87 Wm-1K-1, which is far less than the thermal conductivity of traditional bulk TiS2 thermoelectric materials of 6.8 Wm-1K-1.3. Lastly, based on the above of 1, the obtained Te nanowires were used as in-situ templates. We successfully synthesized Te/TiS2 core-shell heterostructure nanocables. It works on controlled synthesis and transport properties of Te/TiS2 core-shell heterostructure nanocables. The morphologies and structural properties of the as-prepared Te/TiS2 nanocables were investigated by scanning electron microscopy(SEM), and transmission electron microscope(TEM). The chemical composition characterization of the Te/TiS2 nanocables were determined by energy-dispersive spectroscopy(EDS). Due to the formation of high-quality interfacial structure, heterostructure nanocables showed an ultralow thermal conductivity and enhanced seebeck coefficient behavior. The enhanced TE performance(ZT= 2.79) at 212 K from a single nanoccable with diameter of 60 nm was observed because of hetero-phase core/shell structure formed during synthesizing, for example. This is an important step for developing the new generation of high property noval–structured thermoelectric materials in the near future.