Abstract Although the mechanical strength of n-type polycrystalline Bi2Te3 based alloys prepared by conventional powder metallurgy technology is good, its thermoelectric properties have poor repeatability and contamination is introduced. In this work, n-type polycrystalline Bi2Te3 based alloys with uniform microstructure were fabricated by applying equal channel angular extrusion (ECAE) method to extrude the cast ingot directly for four passes at 783 K. The initial lamellae coarse grains with hundreds of microns were broken down efficiently and refined uniformly to only 10–20 μm. And the Vickers hardness was increased by 2.3 times due to the refined grains. On the other hand, it is noteworthy that the ECAE process is also an ideal method to improve the thermoelectric properties of cast ingot by boosting electrical transport properties due to the donor like effect induced by heavy deformation and reducing thermal transport properties due to the enhanced phonon scattering. In order to further optimize the thermoelectric performance, BiCl3 doping was used to precisely tune the carrier concentration to the best range. The intrinsic excitation temperature of Bi2Te3 based alloys gradually shifted from low temperature (below 303 K) to high temperature (463 K) owing to the increased carrier concentration. Finally, the extruded Bi2Te3 based alloy doped with 0.064 wt % BiCl3 obtained the maximum dimensionless figure of merit (ZT) of 0.68 at 423 K, which was far higher than the nearly zero of the initial cast ingot.

中文翻译：

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等通道角挤压：一种细化铸造 n 型 Bi2Te3 基铸锭显微组织以协同优化热电和机械性能的有效方法

摘要 常规粉末冶金技术制备的n型多晶Bi2Te3基合金的机械强度虽好，但其热电性能重复性差，且存在污染。在这项工作中，采用等通道角挤压 (ECAE) 方法在 783 K 下直接挤压铸锭四道次，制备了具有均匀组织的 n 型多晶 Bi2Te3 基合金。初始片晶粗晶粒数百微米被破坏有效且均匀地细化至仅 10-20 μm。由于晶粒细化，维氏硬度提高了2.3倍。另一方面，值得注意的是，ECAE 工艺也是一种改善铸锭热电性能的理想方法，它可以通过重变形引起的施主样效应提高电传输性能，并由于声子散射增强而降低热传输性能。为了进一步优化热电性能，使用 BiCl3 掺杂将载流子浓度精确调整到最佳范围。由于载流子浓度的增加，Bi2Te3 基合金的固有激发温度逐渐从低温（低于 303 K）转移到高温（463 K）。最后，掺杂 0.064 wt% BiCl3 的挤压 Bi2Te3 基合金在 423 K 下获得了 0.68 的最大无量纲品质因数 (ZT)，远高于初始铸锭的几乎为零。