Solid-State Bonding of Bulk PbTe to Nickel Electrode for Thermoelectric Modules

Abstract

The efficiency of thermoelectric generators is defined by the thermoelectric performance of materials, as expressed by the thermoelectric figure-of-merit, and their contacts with electrodes. Lead chalcogenide thermoelectric materials, and in particular PbTe, perform well in the 500-900 K temperature range. Here, we have successfully bonded bulk PbTe to Ni electrode to generate a diffusion barrier, avoiding continuous reaction of the thermoelectric legs and conducting electrodes at the operating temperature. We have modified the commonly used spark plasma sintering assembly method to join Ni electrode to bulk PbTe by driving the total supplied electrical current through the Ni and PbTe solid interfaces. This permits the formation of a thin diffusion layer, roughly 4.5 µm in thickness, which is solely 2 comprised of nickel telluride. This new technique towards the bonding of PbTe with the electrode is beneficial for thermoelectric materials, since high temperatures have proven to be damaging to the quality of bulk material. The interphase microstructure, chemical composition, and crystallographic information were evaluated by a scanning electron microscope equipped with electron back-scattered diffraction analysis. The obtained phase at the Ni/PbTe contact is found to be β 2 Ni 3±x Te 2 with a basic tetragonal crystallographic structure of the defective Cu 2 Sb type.

On the relevance of point defects for the selection of contacting electrodes: Ag as an example for Mg2(Si,Sn)-based thermoelectric generators

“…In fact, finding suitable contacts is a material specific problem, as the outcome will depend on the TE material, the metallic electrode and the potential interactions between them (CTE, adhesion, diffusion, reaction …). Among others, Ni [10,11] and Fe [12] were studied with PbTe showing good bonding results thin interface layers and low electrical contact resistances, Ti [13] and Fe-Ni [14] were successfully tested for skutterudites materials, and Mo [15] and Ag [16] were used with half-heusler systems.…”

Enhanced Performance of Monolithic Chalcogenide Thermoelectric Modules for Energy Harvesting via Co-optimization of Experiment and Simulation

“…As shown in Figure 4b−e, n-and p-type regions and insulator regions are assembled according to our design; fair interfaces among the three material regions are clearly observed with no serious interlayer diffusion even after several tests being performed, as illustrated in Figure S3. In terms of electrode contact, Ni electrodes exhibit good ohmic contact with both n-and p-type materials; the contact resistance factor of Ni and chalcogenide TE materials is extremely low (0.215 ohm cm −2 ); 29,30 the conceivable contact resistance in our TEG (with 1.5 × 1.5 mm 2 Ni electrode area) is as small as ∼4.84 × 10 −3 ohm, which is negligible under the internal resistance of TEG (∼0.15 ohm). As discussed above, Ag 2 S spacers work well for isolation.…”

Challenges and Progress in Contact Development for PbTe‐based Thermoelectrics

“…These are the primary selection criteria for thermoelectric materials in general [24,25] . For the development of PbTe‐based thermoelectric modules, various metals, alloys, and compounds have been tested as contact materials, including Al, [38–40] Ti, [41] Fe, [19–23,29,31,38,42–53] Co, [48,54–57] Co 80 Fe 20 , [14,17,31,58–61] Ni, [29,38,48,49,51,54,56,57,62–67] Cu, [56,57,68] Nb, [69,70] Mo, [29,49,70,71] Ag, [68,72] Ta, [18,70,73,74] and W [18,70,73–76] as well as SnTe, [29,38,43,62] metallic glass, [41] stainless steel [22,77,78] and FeTe [79] . The CTE of PbTe and candidate contact materials are listed in Table 1.…”

“…Ni‐based contacts, which are widely used in bismuth telluride modules, [104] have been studied for the use as contact materials for PbTe [29,38,48,49,51,54,56,57,62–67] . The CTE of Ni (∼13.3×10 −6 K −1 at 273–373 K [89] ) is slightly higher than that of of Co [89] and Fe [90] (∼6–12% respectively), but significantly lower than the CTE of PbTe.…”

“…[17,37] These are the primary selection criteria for thermoelectric materials in general. [24,25] For the development of PbTe-based thermoelectric modules, various metals, alloys, and compounds have been tested as contact materials, including Al, [38][39][40] Ti, [41] Fe, [19][20][21][22][23]29,31,38,[42][43][44][45][46][47][48][49][50][51][52][53] Co, [48,[54][55][56][57] Co 80 Fe 20 , [14,17,31,[58][59][60][61] Ni, [29,38,48,49,51,54,56,57,[62][63]…”