Equal Channel Angular Extrued Bi&lt;SUB&gt;0.5&lt;/SUB&gt;Sb&lt;SUB&gt;1.5&lt;/SUB&gt;Te&lt;SUB&gt;3&lt;/SUB&gt; Thermoelectric Compound

Lim, Chang Hwy; Kim, Kyung Taek; Kim, Yonghwan; Lee, Chang-Hun; Lee, Chihwan

doi:10.2320/matertrans.mep2007297

Cited by 5 publications

(1 citation statement)

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“…The same is true with the ECAE experiments performed by Fan et al 47) in 2008, as well as by Hayashi et al carried out in 2006 48) and 2010 49) although in the latter work they tried to optimize the ECAE route with regard to a (00ℓ) texture for the sake of maximizing the electrical conductivity. In 2008 another treatise concerning ECAE processed Bi 0.5 Sb 1.5 Te 3 compound was undertaken by Lim et al 50) at temperatures 653733 K arriving at a still considerable grain size of about 10 µm which explains that the figure of merit reached the same values as did the previous ECAP works i.e. ZT = 0.9 at RT.…”

Section: Bismuth Telluridesmentioning

confidence: 92%

The Effect of Severe Plastic Deformation on Thermoelectric Performance of Skutterudites, Half-Heuslers and Bi-Tellurides

2019

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Although thermoelectric materials with a figure of merit, ZT, higher than 1.2 have gained considerable interest in electric power generation, little is hitherto known on the influence of severe plastic deformation on thermoelectric performance. Severe plastic deformation is one of the elegant techniques to furnish ultrafine grained microstructure with a high level of point, linear and surface defects. Particularly the phonon scattering on these defects is used as a main route to reduce thermal conductivity in thermoelectric materials and -as a consequence -increasing ZT.The present article provides an overview on the achievements of the various techniques of severe plastic deformation to gain high figures of merit in the thermoelectric materials, commonly used in energy conversion devices, such as skutterudites, clathrates, Heusler phases, and bismuth tellurides.For all skutterudites, high pressure torsion, as one of the major techniques of severe plastic deformation processes, is a great tool to either enhance ZT of hot pressed samples or to directly produce fast and easily high ZT thermoelectric bulks. A still unsurpassed highlight is the enhancement of ZT from 1.6 to almost 2 (Sr 0.09 Ba 0.11 Yb 0.06 Co 4 Sb 12 ) at 825 K.Whilst for thermoelectric clathrates so far little success was reported, high pressure torsion treatment of Heusler and Half-Heusler phases in some cases was able to boost ZT (VTa 0.05 Fe 2 Al 0.95 , rising ZT from 0.22 to 0.3) although the absolute ZT increases are still disappointing. For p-and n-type Half-Heusler alloys (NbFeSb-and TiNiSn-based) at least three temperature cycles are necessary to gain a thermally stable state, indicating that obviously the introduced defects and structure changes are more resistant against heat treatments than in case of skutterudites.Bismuth tellurides of type V 1 (VI) 1 and/or V 2 (VI) 3 (V, VI denote the group elements) have been already deformed by high temperature pressure or high temperature extrusion before the SPD methods were known, for the sake of improving ZT at least with temperatures 300500 K, at most fighting with the condition to achieve a high electrical conductivity because of the strong anisotropy in these materials. By starting with ball milling followed by high temperature pressing at not too high temperatures, not only the electrical conductivity could be kept large but also the lattice thermal conductivity was diminished such that figures of merit up to ZT = 1.4 at T = 373 K were achieved. This value could be reached by many of the ECAP experiments published so far, although only across the sample long axis because of lattice anisotropy. First applications of HPT did not reach that ZT level as either the conditions of texture could be not fulfilled, or, above all, the processing rates and/or temperatures were too high. Recent investigations not having involved SPD found the importance of the lattice defects' specific phonon scattering efficiencies, especially that of dislocations, and by introducing them in sufficiently high densities,...

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