Properties of HPT-Processed Large Bulks of p‑Type Skutterudite\nDD0.7Fe3CoSb12 with ZT > 1.3

0542769 - ÚFM 2022 RIV US eng J - Journal Article
Rogl, G. - Renk, O. - Ghosh, S. - Mallik, R.Ch. - Grytsiv, A. - Buršík, Jiří - Schafler, E. - Tuomisto, F. - Bauer, E. - Rogl, P.F.
Properties of HPT-Processed Large Bulks of p‑Type Skutterudite
DD0.7Fe3CoSb12 with ZT > 1.3.
ACS Applied Energy Materials. Roč. 4, č. 5 (2021), s. 4831-4844. ISSN 2574-0962
Institutional support: RVO:68081723
Keywords : skutterudites * thermoelectrics * nanostructures * high - pressure torsion * severe plastic deformation
OECD category: Condensed matter physics (including formerly solid state physics, supercond.)
Impact factor: 6.959, year: 2021
Method of publishing: Open access
https://pubs.acs.org/doi/10.1021/acsaem.1c00409

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 DD0.7Fe3CoSb12. 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 X-ray 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.

Permanent Link: http://hdl.handle.net/11104/0320618