To achieve high-performance thermoelectric (TE) devices, constructing a good interfacial connection between TE materials and electrodes is as important as having high figure-of-merit TE materials. Although CoSb 3 -based TE devices have received great attention for power generation recently, the limited long-term service stability is the main obstruct for their applications. In this work, we have prepared two kinds of Ti-based alloys (Ti 83.7 Al 10.7 Si 5.6 and Ti 74 Ni 26 ) as the diffusion barrier layer of CoSb 3 -based TE joints by the spark plasma sintering method and have systematically investigated their interfacial behaviors during the aging process. The performances of contact resistivity and mechanical strength for Ti 74 Ni 26 /Yb 0.4 Co 3.8 Fe 0.2 Sb 12 TE joints are good before aging treatment but gradually deteriorate during the aging process, which should be ascribed to the phase-transition-induced negative thermal expansion in Ti−Ni alloys. On the other hand, Ti 83.7 Al 10.7 Si 5.6 /Yb 0.4 Co 3.8 Fe 0.2 Sb 12 TE joints show both low contact resistivity (<10 μΩ•cm 2 ) and high mechanical strength (>20 MPa) before and after 16-day aging at 500 °C, which is originated from the matching of the coefficient of thermal expansion (CTE) and the formation of network structures in Ti−Al−Si alloys. We have also prepared an eight-couple TE module of p-Ge 0.9 Sb 0.1 TeB 0.01 /n-Yb 0.4 Co 3.8 Fe 0.2 Sb 12 and have measured its corresponding device performance. Our work has demonstrated that the matched CTE and network structures in the Ti−Al−Si alloy are key to obtain high-performance CoSb 3 -based TE joints for long-term service.
To
build high-performance thermoelectric (TE) devices for power
generation, a suitable diffusion-barrier layer between the electrodes
and the TE materials in a TE device is generally required for achieving
good interfacial connection with high reliability, high mechanical
strength but low electrical and thermal contact resistivities. GeTe-based
materials have attracted great attention recently due to their high
TE performance in the mid-temperature range, but studies on their
TE devices are still limited. Here, we selected the Al66Si34 alloy as a diffusion barrier for GeTe-based TE legs
based on the matching test of the coefficient of thermal expansion.
The good connection between Al66Si34 and Ge0.9Sb0.1TeB0.01 is realized by the interfacial
reaction, where the randomly distributed Al2Te3 and Ge precipitates are formed at the interface of the joint. The
as-prepared interfacial electrical contact resistivity can be as low
as 20.7 μΩ·cm2 and only slightly increases
to 26.1 μΩ·cm2 after 16 days of aging
at 500 °C. Moreover, the shear strength of the joints can be
as high as 26.6 MPa and unexpectedly increases to 41.7 MPa after 16
days of aging. The thickness of the reaction layer tends to be stabilized
after 8 days of aging and nearly does not change after further aging
to 16 days, which may be ascribed to the drag effect from Si and the
secondary Ge phases. These results demonstrate the great potential
of the Al–Si alloy as a diffusion barrier for GeTe-based TE
devices with high performance.
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