Abstract
In thermoelectric (TE) generators, maximizing the efficiency of conversion of direct heat to electricity requires the reduction of any thermal and electrical contact resistances between the TE legs and the metallic contacts. This requirement is especially challenging in the development of intermediate to high-temperature TE generators. PbTe-based TE materials are known to be highly efficient up to temperatures of around 500 °C; however, only a few practical TE generators based on these materials are currently commercially available. One reason for that is the insufficient bonding techniques between the TE legs and the hot-side metallic contacts. The current research is focused on the interaction between cobalt-metallized n-type 9.104 × 10−3 mol % PbI2-doped PbTe TE legs and the Ag0.32Cu0.43In0.25 brazing alloy, which is free of volatile species. Clear and fine interfaces without any noticeable formation of adverse brittle intermetallic compounds were observed following prolonged thermal treatment testing. Moreover, a reasonable electrical contact resistance of ~2.25 mΩmm2 was observed upon brazing at 600 °C, highlighting the potential of such contacts while developing practical PbTe-based TE generators.
Highlights
Thermoelectric (TE) devices capable of converting waste heat into useful electricity are being constantly investigated for various applications involving different temperature ranges. p-type Bix Sb2-x Te3 [1,2,3,4,5,6] and n-type Bi2 Te3-x Sex [7,8,9,10,11] alloys are the most commonly investigated for operating temperatures of up to 300 ◦ C, while for temperatures beyond 500 ◦ C, filled skutterudites [12,13], half-Heusler [14], and silicide-based [15] compositions are the main focus
The metallic nature of the Ag0.32 Cu0.43 In0.25 brazing alloy and the cobalt contact layer, compared to the semiconducting nature of the TE element, can be observed by the low α and ρ (Figure 3a,b, respectively) and the high κ (Figure 3c) values of these compositions. These results clearly indicate the high potential of the brazing material and the cobalt contact layers to exhibit very low electrical and thermal contact resistances while being applied in TE devices
For increasing the technology readiness level (TRL) of TE converters, based on the widely investigated highly efficient PbTe compound, the current research focused on bonding n-type
Summary
Thermoelectric (TE) devices capable of converting waste heat into useful electricity are being constantly investigated for various applications involving different temperature ranges. p-type Bix Sb2-x Te3 [1,2,3,4,5,6] and n-type Bi2 Te3-x Sex [7,8,9,10,11] alloys are the most commonly investigated for operating temperatures of up to 300 ◦ C, while for temperatures beyond 500 ◦ C, filled skutterudites [12,13], half-Heusler [14], and silicide-based [15] compositions are the main focus. NASA has employed TE devices for deep space missions, such as the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) based on n-type PbTe and p-type PbSnTe [40,41,42], alternatives are still required for developing highly efficient devices by deep investigation in this field. TE elements to create SnTe, which harms the reliability of the TE device [38] For these reasons, a metallized contact layer between the TE elements and the brazing material is frequently required. A metallized contact layer between the TE elements and the brazing material is frequently required For such contact layers, materials with high thermal and electrical conductivities are favorable with respect to device performance.
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