HPT production of large bulk skutterudites

Rogl, Gerda; Ghosh, Sanyukta; Renk, Oliver; Grytsiv, A.; Schafler, Erhard; Zehetbauer, M.; Mallik, Ramesh Chandra; Bauer, E.; Rogl, P.

doi:10.1016/j.jallcom.2020.156678

Cited by 12 publications

(19 citation statements)

References 42 publications

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“…We observed such a behavior already in former investigations on smaller skutterudite specimens. 40,41,[43][44][45][46]55 For all samples, the dislocation density does not differ much among the various samples (Figure 7c). The dislocation density of the HP powder is more or less in the same range as the dislocation density in the center of the HPT-deformed samples.…”

Section: Resultsmentioning

confidence: 92%

“…Depending on the shear strain introduced, that is, the position of the measured specimen in the large HPT disc, ZTs between 0.9 and ∼2.1 were achieved for the samples with a 1 mm thickness. 45 As a first success, a big sample with a thickness of 8 mm and a mass of ∼53 g was HPT-consolidated, revealing an almost homogeneous shear strain and ZTs between 1 and 1.4, 46 leading to the current work, that is, transferring this knowledge to p-type skutterudites.…”

Section: Introductionmentioning

confidence: 86%

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Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3

Renk

Ghosh²,

Mallik³

et al. 2021

ACS Appl. Energy Mater.

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The influence of shear strain on the microstructural, physical, and mechanical properties was studied on large bulk samples (diameter: 30 mm, thickness: 1 or 8 mm), which were consolidated by high-pressure torsion (HPT) from a commercial powder DD 0.7 Fe 3 CoSb 12 . Particularly, the thick sample (mass ∼ 53 g) allowed measuring the thermoelectric (TE) properties with respect to various orientations of the specimen in the sample. All data were compared with those of a hot-pressed (HP) reference sample, prepared with the same powder. Transmission electron microscopy, as well as Xray powder diffraction profile analyses, Hall measurements, and positron annihilation spectroscopy, supported these investigations. Furthermore, synchrotron data for the temperature range from 300 to 825 K were used to evaluate the changes in the grain size and dislocation density as well as the thermal expansion coefficient via the change in the lattice parameter during heating. In addition, hardness and direct thermal expansion measurements of the HPT samples were performed and compared with the HP reference sample's values. With the increase of the shear strain from the center to the rim of the sample, the electrical resistivity becomes higher, whereas the thermal conductivity becomes lower, but the Seebeck coefficient remained almost unchanged. For the thin as well as thick samples, the enhanced electrical resistivity was balanced out by a decreased thermal conductivity such that the maximum ZT values (ZT = 1.3−1.35 at 856 K) do not vary much as a function of the shear strain throughout the sample, however, all ZTs are higher than that of the HP sample. The thermal−electric conversion efficiencies are in the range of 14−15% (for 423−823 K). With similar high ZT values for the n-type skutterudites, fabricated in the same fast and sustainable way, these p-and n-type skutterudites may serve as legs for TE generators, directly cut from the big HPT bulks.

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Section: Resultsmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 86%

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3

Renk

Ghosh²,

Mallik³

et al. 2021

ACS Appl. Energy Mater.

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“…The "big" samples were processed in a custom-built equipment from Klement, Austria, outfitted with an induction heating system from IEW Corporation. The powder was filled into a hollow copper cylinder (wall thickness 1 mm) with an inner diameter of 30 mm and a height of 2, 3 or 16.5 mm (placed on the lower anvil) and subsequently compacted under a nominal pressure of 5 GPa, heated to 250°C or 300°C (15 min holding time) before the pellet was deformed at a rotational speed of 0.2 rpm for 0.13, one or five revolutions (details are given in references (Rogl et al, 2020b)).…”

Section: Severe Plastic Deformation Via High Pressure Torsionmentioning

confidence: 99%

“…In an additional step this sustainable and fast method has been scaled up to produce bulk p-and n-type skutterudites of larger sizes (disks with a diameter of 30 mm and a height of 1 or even 8 mm). ZTs were in about the same range or even higher than for the small samples, the production time was between 30 and 50 min and the big samples with a weight of about 50 g turned out to be homogeneous and could therefore directly be used to cut legs for TE modules (Rogl et al, 2020b). A further upscale of this fast and sustainable production method (disks with a diameter of 10 cm and various heights), using commercial p-and n-type skutterudite powder is planned.…”

Section: Introductionmentioning

confidence: 99%

How Severe Plastic Deformation Changes the Mechanical Properties of Thermoelectric Skutterudites and Half Heusler Alloys

Rogl

2020

Front. Mater.

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Thermoelectric leg materials with a high figure of merit, ZT, are the essential basis to build thermoelectric generators, directly converting waste heat into electricity. Skutterudites and half-Heusler alloys are promising candidates because they can be used in a wide temperature range, the starting material is available and cheap and in addition they are environmentally friendly. Severe plastic deformation via high-pressure torsion (HPT) is a technique to achieve very fine grains in micro- or even nano size with small and high angle grain boundaries and in parallel introduces a high level of defects like vacancies and dislocations. Therefore, this method was applied not only to enhance ZT of ball-milled and hot-pressed skutterudites and half-Heusler alloys but so far was also successful to directly produce dense nanostructured bulks from skutterudite powders. Although HPT compacted samples are chemically homogeneous, they are not homogeneous with respect to the shear strain increasing from the center to the rim. HPT changes the microstructure and density and thereby not only influences the thermoelectric but also the mechanical properties. In this work an overview is given of the influence of HPT on hardness, elastic moduli, indentation fracture toughness, thermal expansion and thermal shock resistance. The corresponding properties of hot-pressed skutterudites and half-Heusler alloys are compared with those after severe plastic deformation, dependent on the processing properties and position of the specimen in respect to shear strain. Data are collected from earlier investigations of the authors and from the literature, but also newly achieved and evaluated data are included.

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“…[26,27] Moreover, severe plastic deformation (SPD) and sonication have been utilized to produce ultrafine grains and a higher concentration of structural defects, e.g., grain boundaries, vacancies, and dislocations, to reduce the thermal conductivity and increase the Seebeck coefficient. [28][29][30][31] However, the SPD method has been used mostly in skutterudites, half-Heusler, and lead telluride alloys, and sonication methods have been mostly applied to oxide-based TE materials and organic/ inorganic nanocomposites. There are limited reports on the production of nanostructured BiSbTe alloys by SPD or sonication DOI: 10.1002/adem.202100955 Nanoengineering of thermoelectric (TE) materials is an effective approach to decouple their electronic and thermal transport properties, hence enhancing their TE efficiency.…”

Section: Introductionmentioning

confidence: 99%

Nanoengineering Approaches to Tune Thermal and Electrical Conductivity of a BiSbTe Thermoelectric Alloy

Masoumi

Pakdel

2021

Adv Eng Mater

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Nanoengineering of thermoelectric (TE) materials is an effective approach to decouple their electronic and thermal transport properties, hence enhancing their TE efficiency. Nanoengineering strategies can significantly reduce the thermal conductivity through the corporation of different phonon scattering mechanisms, whereas the electrical conductivity may not be affected considerably. Herein, the effects of three nanoengineering approaches on the structural, electrical, and thermal properties of Bi0.5Sb1.5Te3 (BST) alloy are compared: (a) nanohybridization of the alloy by adding Sb2O3 nanoparticles, (b) severe plastic deformation via high‐pressure torsion, and (c) grain refinement by sonication of BST powders before sintering. It is shown that among these methods, severe plastic deformation induces ultrafine grains and a high density of dislocations, resulting in a large reduction of the total thermal conductivity (32.8%) and a moderate decline in the electrical conductivity of (15.7%) at 300 K. A notable decrease in the lattice thermal conductivity (56.8% at 300 K) is attributed to midfrequency phonon scattering by the dislocations together with low and high frequency scatterings through grain boundaries and point defects, respectively. A new pathway is opened for designing highly efficient TE materials through nanoengineering approaches, particularly severe plastic deformation.

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HPT production of large bulk skutterudites

Cited by 12 publications

References 42 publications

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3

How Severe Plastic Deformation Changes the Mechanical Properties of Thermoelectric Skutterudites and Half Heusler Alloys

Nanoengineering Approaches to Tune Thermal and Electrical Conductivity of a BiSbTe Thermoelectric Alloy

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HPT production of large bulk skutterudites

Cited by 12 publications

References 42 publications

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD0.7Fe3CoSb12 with ZT > 1.3

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD0.7Fe3CoSb12 with ZT > 1.3

How Severe Plastic Deformation Changes the Mechanical Properties of Thermoelectric Skutterudites and Half Heusler Alloys

Nanoengineering Approaches to Tune Thermal and Electrical Conductivity of a BiSbTe Thermoelectric Alloy

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Product

Resources

About

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3

Properties of HPT-Processed Large Bulks of p-Type Skutterudite DD_0.7Fe₃CoSb₁₂ with ZT > 1.3