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Abstract:Recently, SnSe material with an outstanding high ZT (Figure of merit) of 2.6 has attracted much attention due to its strong applicability for highly efficient thermoelectric devices. Many studies following the first journal publication have been focused on SnSe materials, not on thermoelectric devices. Particularly, to realize highly efficient intermediate-temperature (600~1000 K) thermoelectric modules with this promising thermoelectric material, a more thermally and electrically reliable interface bonding technology needs to be developed so that the modules can stably perform their power generation in this temperature range. In this work, we demonstrate several approaches to develop metallization layers on SnSe thermoelectric legs. The single-layer metallization shows limitations in their electrical contact resistances and elemental diffusions. The Ag/Co/Ti multi-layer metallization results in lowering their electrical contact resistances, in addition to providing more robust interfaces. Moreover, it is found to maintain the interfacial characteristics without any significant degradation, even after heat treatment at 723 K for 20 h. These results can be effectively applied in the fabrication of thermoelectric devices or modules that are made of the SnSe thermoelectric materials.

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Plasma sprayed ceramic coating layers were investigated for use in suppressing the oxidation and sublimation of intermediate temperature PbTe thermoelectric legs (usually operated in the temperature range of 300–700 °C). The authors used two different oxides for the comparison of their antioxidation characteristics. One is yttria (Y2O3) and the other is 8 mol. % yttria-stabilized zirconia [(Y2O3)0.08(ZrO2)0.92, YSZ]. Both oxides were coated by plasma spray method on the surfaces of the PbTe thermoelectric legs, respectively. As a result, the Y2O3 coating layers could not prevent the progression of oxidation in the thermoelectric PbTe surfaces at 500 °C, but the YSZ coating layers showed a relatively high resistance enough to prevent the progression of oxidation, which is promising for intermediate-temperature thermoelectric modules. The x-ray diffraction and x-ray photoelectron spectroscopy investigations revealed that the YSZ-coating of PbTe thermoelectric legs led to the formation of the secondary oxide phase layers that help to prevent the oxidation during the heat treatment. Overall, the reliability and electrical properties of the YSZ-coated PbTe thermoelectric legs were investigated. Finally, the authors expect that this work will be useful for the future intermediate-temperature thermoelectric modules in the future.

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