Influence of shear strain on HPT-processed n-type skutterudites yielding ZT=2.1
Influence of shear strain on HPT-processed n-type skutterudites yielding ZT=2.1
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DOI：
10.1016/j.jallcom.2020.157409
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发表时间：
2021-02
影响因子：
6.2
通讯作者：
G. Rogl;Sanyukta Ghosh;Oliver Renk;K. Yubuta;A. Grytsiv;E. Schafler;M. Zehetbauer;R. Mallik;E. Bauer;P. Rogl
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文献类型：
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作者：
G. Rogl;Sanyukta Ghosh;Oliver Renk;K. Yubuta;A. Grytsiv;E. Schafler;M. Zehetbauer;R. Mallik;E. Bauer;P. Rogl
本文以工业粉末为原料，采用冷压(CP)和高压扭转(HPT)工艺成功地制备了具有高ZTS的方铅矿。本文通过对(Sm，mm)0.15Co4Sb12高压扭转圆盘不同位置切制样品的分析，详细研究了剪切应变和制备参数，特别是温度对(Sm，mm)0.15Co4Sb12高温扭转圆盘的微观结构、热电性能和力学性能的影响。在这些大圆盘(直径30 mm，厚度约1 mm)上，剪切应变γ从样品中心到边缘呈线性上升，达到γ-∼-450(5转)，这是首次在Skutterudite中实现的值。HPT应变是引入高密度晶格缺陷的关键，特别是位错，这会导致显著的晶粒细化。由于加工温度主要影响HPT固结样品的密度，从而影响其物理和力学性能，因此，施加的剪切应变决定了热电参数。作为一个重要特征，塞贝克系数在应变下基本保持不变。尽管剪切应变的增加导致导热系数显著降低，但这一有利的效应伴随着电阻率的显著增加。因此，这两个有争议的影响的相互作用导致了最大和创纪录的热电优值系数ZT∼2.1。
After our successful new and energy-saving production route to prepare bulk skutterudites with high ZTs from commercial powders via cold pressing (CP) and high-pressure torsion (HPT), we present in this paper a detailed study of the influence of shear strain and the preparation parameters, especially the temperature, on the micro-structural, thermoelectric and mechanical properties by analyzing specimens cut from various positions of the HPT disks of (Sm,Mm)0.15Co4Sb12. Across these large discs (30 mm in diameter and about 1 mm thickness) the shear strain γ rises linearly from the center of the sample to the rim reaching γ ∼ 450 (for 5 revolutions), a value first time realized for skutterudites. HPT-straining is essential for the introduction of high densities of crystal lattice defects, particularly dislocations, which result in a significant refining of the grains. Whereas the processing temperature mainly influences the density of the HPT consolidated samples and as a consequence, physical and mechanical properties, the applied shear strain rules the thermoelectric parameters. As an important feature, the Seebeck coefficient remained roughly unchanged under strain. Although the increasing shear strain caused the thermal conductivity to significantly decrease, this beneficial effect is accompanied by a concomitant significant increase of the electrical resistivity. Consequently, the interplay of the two controversial influences results in a maximum and record high thermoelectric figure of merit ZT ∼2.1.