Properties Of Composite Layered Oxide Thermoelectric Materials

Since the industrial revolution, because of the rapid development of human society, demand for energy is increasing, while the rapid development of the industry also makes the increasingly serious environmental pollution. Thus, environmentally friendly renewable energy technologies become concerned about the hot research, among which thermoelectric conversion technology is highly expected. The investigation of thermoelectric materials focus on new thermoelectric materials and how to improve ZT base on some potential thermoelectric materials. Composite is also an effective path for improving thermoelectric property. Subject of the present paper is several layered oxide thermoelectric materials, including BiCuXO (X= Se, Te) and Bi2Sr2Co2Oy materials systems. The ZT values of the two thermoelectric materials are not high because it’s restricted by their thermoelectric parameters. Wherein due to the low electrical conductivity of BiCuSeO, resulting in poor thermoelectric performance, and the high thermal conductivity of Bi2Sr2Co2Oy, we use compositing methods to optimize the electrical conductivity or thermal conductivity of these two materials, and study their thermoelectric performance. The main research works are described as follows:1. thermoelectric properties of BiCuTeO and BiCuSeO compositeWe compare the electrical transport properties of BiCuXO (X=Se, Te) ceramics before and after ball-milling, showing ball-milling can improve the electrical conductivity of the ceramic samples. The study of (1-x)BiCuSeO+xBiCuTeO composite ceramics shows, with the increase of BiCuTeO component, the electrical conductivity of the sample has been greatly improved, which is because BiCuTeO’s conductivity is relatively high, reasulting in increasing carrier concentration, thereby increasing the conductivity, so the ZT value of 0.9BiCuSeO+0.1BiCuTeO has been greatly improved compared with BiCuSeO. However, due to the low Seebeck coefficient of BiCuTeO, the ZT value of 0.1BiCuSeO+0.9BiCuTeO changed little compared with BiCuSeO.2. thermoelectric properties of Bi2Sr2Co2Oy and carbon composite(1-x)Bi2Sr2Co2Oy+xC single crystals are grown through optical floating zone method. The study shows, after compositing carbon nanotubes and porous carbon, the thermal conductivity of both composites are reduced. This is because carbon materials have large gaps, enabling atomics to vibrate in the gaps, resulting in improving the ability of the lattice phonon scattering, thereby reducing the lattice thermal conductivity. However, the electrical conductivity is reduced by several orders of magnitude, because the electrical conductivity of carbon nanotubes and porous carbon are pretty low, leading to reduce the carrier mobility.Through these studies, we have a better understanding of BiCuXO (X= Se, Te) and Bi2Sr2Co2Oy materials systems. For BiCuXO (X= Se, Te) system, the thermoelectric performance can be improved through compositing, but the amount of compotents should be appropriate. The key issue is to grasp the balance of electrical conductivity and Seebeck coefficient. We could change several times the amount of compotents, so we can find the best combination to maximize the power factor. For (1-x)Bi2Sr2Co2Oy+xC system, we could composite alkylene carbon materials. Because the electrical conductivity of this kind of materials is very good, the thermal conductivity can be reduced while improving the electrical conductivity, thereby the thermoelectric properties of Bi2Sr2Co2Oy system is improved.