Creep Deformation Of Thermoelectric Materials
Loading...
Date
2023-06-16
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ProQuest
Abstract
As more thermoelectric materials/devices make it into the market for various applications, several
aspects need to be explored and optimized, beyond simply targeting high conversion efficiency at
the material levels. One critical aspect is the guarantee of mechanical stability at both the material
and the device level, which demands deeper understanding of the stresses affecting a thermoelectric
(TE) material/module and the concomitant mechanical deformation modes. In this thesis, we
elaborated on characterizing the stresses impacting a TE module, both the manufacturing residual
and the operational categories. Such stresses collectively are capable of inducing time-dependent
high-temperature deformation (i.e. creep), which is shown to negatively impact the thermoelectric
performance, seen as a drop in the power factor and the figure of merit zT. Among the mid-high
temperature TE materials tested for creep, the half-Heusler alloy Hf0.3Zr0.7NiSn0.98Sb0.02 depicted
the highest creep resistance reported so far, sustaining stresses up to ∼ 360 MPa at 600 ℃ without
notable failure. The creep resistance of the Skutterudite alloy Yb0.3Co4Sb12 is midway between
that of low-mid temperature TE materials, such as Bi2Te3, PbTe and TAGS-85, and that of midhigh
temperatures thermoelectrics, including silicides and half-Heusler alloys. The in situ electrical
resistivity-creep experiments on doped PbTe confirmed that dislocations multiplication continuously
increases the electrical resistivity in a semi-linear trend with the engineering strain, despite the high
temperature recovery processes. The resistivity increase was seen to be controlled by the rate of
change of the immobile dislocations density with the engineering strain, such dislocations were seen
to form complex networks and subgrain structures, as revealed by TEM analysis. Lastly, in an
effort to explore 3D printability of ternary and multinary TE alloys, the n-type half-Heusler alloy
Nb1-xCoSb was successfully shown to be printable utilizing fully prealloyed powder and saturation
annealing under Sb atmosphere to mitigate issues such as volatility of Sb and porosity. A zTmax ∼
0.1 was achieved at 600 ℃.
Description
Keywords
Thermoelectric, Creep, Conducitivty, 3D printing, Dislocations