| Thermoelectric(TE) materials that can convert thermal energy into electrical energy directly from temperature differences or vice versa are a kind of new function materials. Thermoelectric devices which are made from TE materials have many attractive advantages, such as non-pollution, energy conservation, benign stability,and long life time. They have been widely used in many fields such as cooling and temperature controlling in computers, microelectronics and aerospace. The efficiency of TE materials is judged by their dimensionless figure of merit. The figure of merit ZT of a TE material is defined by2 ZT =a sT/k, where a 、s 、k and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature respectively.At present, Bi2Te3 and its solid solution alloy as the earliest and most mature thermoelectric materials have been widely used in the semiconductor refrigeration components. Bi2Te3 has not been applied in large-scale because its supreme non-dimensional thermoelectric figure of merit is about 1. Consequently, how to improve and optimize the thermoelectric performance becomes a research hotspot around the world. In recent years, the main means to improve the TE properties of TE materials is using energy-band engineering and nanotechnology, which is the main direction in the research of Bi2Te3 materials.This thesis combine nanotechnology with element doping focused on the effect of different element doping on thermoelectric properties of Bi2Te3-based alloys. The main research contents and results are as follows:(1) Lu and I doping were investigated. Hydrothermal method was used to prepare Lux Bi2-x Te3(x=0, 0.1, 0.25 and 0.4) and Bi2Te3-x Ix(x=0、0.05、0.1、0.2)nanopowder. It is shown that element doping has remarkable effects on the morphologies of the nanopowders, it is harmful to the formation of the flower-like nanopowders. The main reason is that the replacing Bi by Lu element can change the bonds strengh and slow the growth rate along a-axis, b-axis, and harm to form larger nanosheets. Because EDTA is beneficial to the growth rate along a-axis and b-axis, we can increase the amount of EDTA appropriately in order to make the Bi2Te3 nanopowders keep flower-like morphologies after doping.(2) The Lu and I doped flower-like nanopowders were hot-pressed into bulk pellets under the appropriate temperature and to study the effects of element dopingon the thermoelectric properties. It is shown that the grains in the bulk samples prepared from the flower-like nanopowders are distributed randomly, having no obvious orientation. And the grains show heterogeneity, few small grains coexisting with large grains. We attributed the good TE properties of such bulk samples prepared from flower-like nanopowders to this microstructure because we believe that such microstructure can effectively scatter phonons but less scatter electric carriers. The results show that lutetium doping can reduce the electric resisitivity greatly, while does not reduce the Seebeck coefficient too much, therefore helps to improve the thermoelectric properties of materials. Especially, Lu0.1Bi1.9Te3 bulk sample can reach1.72 at 373 K, which is a high performance material among the n-type Bi2Te3 semiconductor thermoelectric. And for the Bi2Te2.9I0.1 sample, the Seebeck coefficient and thermal conductivity do not change significantly, but the resistivity is lower than the undoped samples. The Bi2Te2.9I0.1 bulk sample can reach 1.3 at 448 K which is higher than the commercial Bi2Te3 bulk. |
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