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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In this paper, monoclinic SrAl2Si2O8 ceramics with porous structures were prepared based on ion‐exchanged geopolymer precursor technique. Micron‐level pores with a homogeneous pore‐size distribution were introduced into the inorganic framework using foaming agents. The results demonstrated that the apparent density, pore‐size distribution and specific surface area of porous geopolymer precursors can be well‐engineered via tailoring the category and concentration of the foaming agent. After being treated at 900°C, hexagonal SrAl2Si2O8 first‐crystallized from the amorphous geopolymer matrix and then gradually converted into monoclinic SrAl2Si2O8 between 1100°C and 1200°C. The resulting monoclinic SrAl2Si2O8 ceramics maintained the porous structures during high‐temperature treatments and exhibited high porosity, specific surface area, and compressive strength. The aforementioned strategy not only achieves monoclinic SrAl2Si2O8 ceramics with well‐defined and robust microstructures, but also provides an alternative route to prepare other porous ceramics, with potential applications in fields of high‐temperature filters, adsorbents, and heterogeneous catalysis.