熔体旋甩法合成n型(Bi_(0.85)Sb_(0.15))_2(Te_(1-x)Se_x)_3化合物的微结构及热电性能

采用熔体旋甩结合放电等离子烧结(MS-SPS)技术制备了单相n型四元(Bi0.85Sb0.15)2(Te1-xSex)3(x=0.15,0.17,0.19,0.21)化合物,并对所得样品的微结构和热电传输性能进行了系统研究.样品自由断裂面的场发射扫描电子显微镜及抛光面的背散射电子成分分析表明:块体材料晶粒细小,晶粒排列紧密,成分分布均匀且相结构单一,样品中存在大量10—100nm的层状结构.随着Se含量x的增加,样品的电导率和热导率逐渐增加,而Seebeck系数逐渐降低.相比商业应用的区熔材料,MS-SPS方法合成的高Se组成的样品均在425K后表现出更高的ZT值,其中(Bi0.85Sb0.15)2(Te0.83Se0.17)3样品具有最高的ZT值,在360K可达到0.96,并在320—500K均保持较高的ZT值,500K时其ZT值相比区熔材料提高了48%.此外,通过调节Se的含量,可以有效地调控材料的ZT峰值出现的温度段,这对多级或梯度热电器件的制备具有重要意义.

Microstructures and thermoelectric properties of n-type melting spun(Bi0.85Sb0.15)2(Te1-xSex)3 compounds

The single phase n-type (Bi_0.85Sb_0.15)₂(Te_1-xSe_x)₃(x=0.15, 0.17, 0.19, 0.21)compounds have been synthesized by melt-spinning combined with subsequent spark plasma sintering technique, and the microstructures and thermoelectric transport properties of the bulk materials have been systematically investigated. The results of field emitted scanning electron microscopy images show that the bulk materials possess refined crystalline and a large number of layered structures with the sizes from 10 nm to 100 nm, and their differences in composition and phase are detected neither from the back scattering image nor from element face distributing images of polishing surface. With the increase of content of selenium, the electrical conductivity and the thermal conductivity increase but the Seebeck coefficient decreases. Comparing with the traditional zone melted material, the samples with higher selenium content possesse higher thermoelectric optimum value ZT after 420 K and the highest ZT of the sample (Bi_0.85Sb_0.15)₂(Te_0.83Se_0.17)₃ can reach 0.96 at 360 K, whose ZT increases by 48% at 500 K correspondingly. In addition, the temperature of the peak ZT can be adjusted by varying the content of selenium, which is meaningful for the design and the fabrication of multi-scale or grade thermoelectric device.