纳米结构碲化铋合金的制备及电热输运特性

Synthesis and thermoelectric properties of nanostructured bismuth telluride alloys

采用惰性气体保护蒸发-冷凝法制备了纳米Bi及Te粉末,结合机械合金化和放电等离子烧结技术,在不同烧结温度下制备出了单一物相且具有纳米层状结构及孪晶亚结构的n型Bi_2Te_3块体材料,并系统研究了块体材料的晶粒尺度、微结构及其对电热传输特性的影响.SEM,TEM分析结果表明,以纳米粉末为原料,通过有效控制工艺条件,可以制备出具有纳米层状结构Bi_2Te_3合金块体材料,同时纳米层状结构中存在孪晶亚结构;热电性能测试结果表明,具有纳米层状结构及孪晶亚结构的块体试样与粗晶材料相比,热导率大幅度降低,在423 K附近,热导率由粗晶材料的1.80 W/mK降至1.19 W/mK,晶格热导率从1.16 W/mK降至0.61 W/mK,表明纳米层状结构与孪晶亚结构共存,有利于进一步提高声子散射,降低晶格热导率.其中在693 K放电等离子烧结后的试样于423K附近取得最大值的无量纲热电优值(ZT),达到0.74.

The Bi and the Te nano-powders are prepared by inert gas protected evaporation-condensation method;the n-type Bi_2Te_3 bulk materials with nano-layer and twin crystallite sub-structures are then synthesized by mechanical alloying and spark plasma sintering technique.The effects of grain size and microstructure on thermoelectric property are also systematically studied.The SEM and the TEM analyseis show that the nano-layered Bi_2Te_3 bulk materials with twin crystallite sub-structures could be fabricated by controlling the preparing procedures.The thermoelectric property result shows that the thermal conductivity is lowered compared with that of bulk material of coarse-grained starting powders.The thermal conductivity decreases from 1.80 W/mK to 1.19 W/mK at 423 K,the lattice thermal conductivity decreases from 1.16 W/mK to 0.61 W/mK at 423 K,indicating that the phonon scattering could be enhanced due to the coexistence of nano-layer and twin crystallite sub-structures,leading to reduced phonon thermal conductivity.The dimensionless figure of merit ZT reaches 0.74 at 423 K for bulk materials sintered at 693 K.