High pressure torsion, a large‐scale manufacturing tool for high ZT skutterudite thermoelectrics

Abstract

Dedicated to Professor Mercouri Kanatzidis on the occasion of his 65th birthdayFor mass production of thermoelectric generators, a cheap/ sustainable method is required to fabricate leg material with a high figure of merit, ZT. Severe plastic deformation, SPD, increases the defect density, and in parallel decreases the grains to nano-size. SPD via high-pressure torsion, HPT, was used to process hot pressed discs, whereby the Seebeck coefficient remained unchanged and the enhanced electrical resistivity was overcompensated by a low thermal conductivity, resulting in a raise of ZT. Secondly, cold pressed commercial p-and n-type skutterudite-powder was deformed via HPT, exhibiting higher ZT values than the hot-pressed reference samples. This method was upscaled to samples of 30 mm diameter (heights: 1 mm, 8 mm). These large samples, enabled to study the influence of shear strain with all its impact on micro-structural, physical and mechanical properties, revealing for the thin samples record high ZTs. Both thick samples showed homogeneous properties and ZTs ~1.3.

High-Throughput Prediction of the Thermal and Electronic Transport Properties of Large Physical and Chemical Spaces Accelerated by Machine Learning: Charting the ZT of Binary Skutterudites

“…Several methods for synthesizing and processing skutterudites have been reported, leading to significant enhancements in their TE performance. , Techniques such as spark plasma sintering or cold sintering process can tailor the skutterudite microstructure and improve ZT . One of the techniques that has yielded significant improvements is high-pressure torsion, HPT, which introduces many grain boundaries as well as dislocations in the structure, enhancing ZT values up to a factor of 2 for some skutterudites . The methodology used in this study can also take into account the influence of grain boundaries on the electronic and thermal transport properties of materials .…”

Mechanical behaviour of thermoelectric materials – a perspective

“…High-pressure torsion (HPT) deformation is considered one of the successful approaches to induce high dislocation densities to TE materials, in which high strains are attainable with relatively minimal cracking, as opposed by simple tensile or compression deformation [148][149][150][151][152][153][154][155][156][157][158][159][160][161]. In one of the successful applications of HPT, Rogl et al showed that although the high temperature HPT increased significantly the electrical resistivity of impure DD 0.40-Fe 2.8 Co 1.2 Sb 12 (DD stands for didymium, a binary Nd-4.8 wt% Pr alloy), the enhancement in the Seebeck coefficient (120-210 mV/K @ 800 K) and the drop in the thermal conductivity (35-23 mW/cm•K @ 800 K) led to a zT enhancement from 0.5 of the undeformed sample to 1.38 after deformation [153].…”

Some Unresolved Problems of High-Pressure Torsion

“…4) The results of recent studies on the applications of HPT for producing advanced materials of different categories were surveyed in a number of publications. They refer to thermoelectric generators, 5) magnetic materials, 6) high entropy alloys, 7) hydrogen storage materials, 8,9) superconducting materials, 10) semiconductors, 11) and hybrid nanocrystalline alloys. 12) Besides, review articles focusing on various aspects of HPT were published.…”