| Bismuth telluride was the first known narrow gap semiconductor thermoelectric materials.Commercialized Bi2Te3-based alloy is mainly synthesized by zone melt and widely used in semiconductor refrigeration,which is the only commercial TE materials with the best properties near room temperature.But the insufficient mechanical property has been the key to limit the automatic assembly and production of thermoelectric devices and applications in the high-end market,such as micro-electronics and communication electronics.During the past twenty years,in order to improve the mechanical properties and thermoelectric performance of Bi2Te3-based materials,the new preparation technology based on powder metallurgy have been introduced,and obtained good results.In this paper,the influence of different particle size and different dopants on the material performance are compared.Based on this,a large bulk of sample was prepared to repeat the high performance obtained from the small size samples and study the forming technique of micro-thermoelectric arms.The main results are listed as below:1.The particle size in hot pressed has great influence on the transport property and microstructure of material.By controlling the powder particle size,we can regulate the defect concentration introduced during the preparation,and control the influence of donor-like-effect on the properties,which is benefit for keeping the optimal performance near room temperature.At the same time,the powder particle size have great influence on the formation of texture,bigger particle size is beneficial to the texture formation during hot pressing and deforming and the mobility improvement.Finally,high-performance bismuth telluride-based alloys were obtained.Start from zone-melted ignots,the hot-deformated sample showed a maximum zT of?1.0 at approximately 340 K,and the bending strength and compressive strength increased by 350%and 150%respectively.For the ordinary smelting ignots,the peak of zT achieved 1.0 at 350 K when the particle size is at 50?75 ?m.The preparation technology is also suitable for large bulk bismuth telluride-based alloys.2.It can obviously improve the carrier concentration of the bismuth telluride material and improve the thermoelectric properties by doping and alloying.For different ioduret dopants TeI4,MnI2 and SbI3,the cations of dopants not only affect their stability,but also affect their doping efficiency in the matrix.Mn,Sb can replace Bi position,and providing a hole to optimized the carrier concentration,but inducing Te can suppress antisite defect formation effectively in bismuth telluride-based alloys,which can further promote electronic carrier concentration.3.The P-type Bio.5Sb1.5Se3 and N-type Bi2Te2.79Se0.21 bulk materials of 300 g grade were prepared by the powder hot pressing and hot deformation process,which were used to form micro thermoelectric arms.The thermoelectric properties and mechanical properties of the amplifying bulk can repeat the high performance obtained from the samples with small size,and the maximum zT value is 1.2 and 1.0 respectively.At the same time,we explored the forming technique of micro-thermoelectric arms.225 thermoelectric arms were formed on 1 cm2 thermoelectric chip through the mechanical cutting method,which provide reference for micro device manufacturing.Besides,the utilization of materials is improved in the forming process due to the improvement of mechanical property.4.We tried to build thermoelectric devices test system and monitoring the output voltage under of commercial thermoelectric devices.It can produce millivolt level output voltage under natural temperature difference,which can be used for supplying power to micro devices.Thus,we can make full use of the nature heat in this way and optimize the structure of energy. |
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