Half-Heusler alloys: Enhancement of ZT after severe plastic deformation (ultra-low thermal conductivity)

Author(s)
Gerda Rogl, Sanyukta Ghosh, Lei Wang, Jiri Bursik, Andriy Grytsiv, Michael Kerber, Ernst Bauer, Ramesh Chandra Mallik, Xing Qiu Chen, Michael Zehetbauer, Peter Rogl
Abstract

Several n- and p-type Half-Heusler (HH) thermoelectric materials (Ti0.5Zr0.5NiSn-based and NbFeSb-based) have been processed by high-pressure torsion (HPT) to improve their thermoelectric performance via a drastic reduction towards ultra-low thermal conductivity. This reduction occurs due to grain refinement and a high concentration of deformation-induced defects, i.e. vacancies and dislocations as inferred by this severe plastic deformation and documented via SEM and TEM investigations. In most cases the figure of merit, ZT, and the thermo-electric conversion efficiency were enhanced up to η ∼ 10% for the thermally stable HPT-processed sample. Raman spectroscopy, backed by DFT calculations, proves that HPT induces a stiffening of the lattice and as a consequence, a blue-shift of the lattice vibrations occurs. Furthermore for all investigated specimens Vickers hardness values after HPT were significantly higher, whereas the change in the elastic moduli was less than 5% in comparison to the HP reference sample.

Organisation(s)
Department of Materials Chemistry, Physics of Nanostructured Materials
External organisation(s)
Technische Universität Wien, Christian Doppler Laboratory for Thermoelectricity, Indian Institute of Science, Chinese Academy of Sciences (CAS), University of Science and Technology of China (USTC), Czech Academy of Sciences
Journal
Acta Materialia
Volume
183
Pages
285-300
No. of pages
16
ISSN
1359-6454
DOI
https://doi.org/10.1016/j.actamat.2019.11.010
Publication date
01-2020
Peer reviewed
Yes
Austrian Fields of Science 2012
Nanomaterials, Physical chemistry
Keywords
ASJC Scopus subject areas
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Portal url
https://ucris.univie.ac.at/portal/en/publications/halfheusler-alloys-enhancement-of-zt-after-severe-plastic-deformation-ultralow-thermal-conductivity(f8c4dbbd-06ff-47e9-b31c-2781a3d99c78).html