Screening Metal Electrodes for Thermoelectric PbTe

Abstract

Historically, both p- and n-type PbTe show extraordinary thermoelectric figures of merit within 300–600 °C for power generation applications. A full realization of the potential of these high-performance thermoelectric materials on a device level largely depends on the electrical and thermal contacts with the metal electrodes. Chemical inertness with a slow diffusion could be an important criterion for the selection of metal electrodes. In this work, the diffusion of the total 12 potential metal electrodes in PbTe diffusion couples are focused on and sorted, suggesting the superiority of Co as an electrode for its low diffusion coefficient and interfacial contact resistivity, inertial to PbTe and compatibility in temperature for sintering. The strategy used in this work is believed to be applicable to the selection of electrodes for other thermoelectric materials.

Challenges and Progress in Contact Development for PbTe‐based Thermoelectrics

“…While phase diagrams are a powerful tool for determining the chemical stability between PbTe and contact layer materials [82,96–102,105] as functions of temperature and chemical composition, their investigation is time‐consuming. As an alternative, high‐throughput experiments [48] of PbTe/contact material combinations at various annealing temperatures and annealing times can give valuable information in less time to evaluate stability conditions of contact materials, as demonstrated in other thermoelectric materials such as skutterudites [113] . To improve the mechanical stability of the bond between PbTe leg and contact layers, CTE matching should be improved.…”

“…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.…”

“…Co 80 Fe 20 ‐based contact layers, whose CTE (∼12.0×10 −6 K −1 at 300–773 K) [17] lies between that of Co [89] and Fe [90] have been used for the fabrication of PbTe‐based thermoelectric legs and modules [14,17,31,58–61] . Values for ρ c between Co 80 Fe 20 and p‐type PbTe 0.973 Na 0.02 Ge 0.007 Te (∼8×10 −10 Ω m 2 –20×10 −10 Ω m 2 ), [17] n‐type PbTe 0.98 Ga 0.02 Te (∼7×10 −10 Ω m 2 –29×10 −10 Ω m 2 ), [17] and n‐type Pb 0.98 Ga 0.02 Te doped with 3 at.% GeTe (≤10×10 −10 Ω m 2 ) [61] are comparable to PbTe/Co contacts [48,55–57] . Due to the CTE mismatch, crack formation during the co‐sintering of Co 80 Fe 20 with p‐ and n‐type have shown to increase the R in of the legs [17] .…”

“…Fe is a thoroughly studied contact material for PbTe thermoelectric modules [19–23,29,31,38,42–53] . The difference in CTE of metallic Fe (∼11.8×10 −6 K −1 at 300 K [90] ) and PbTe is large.…”

“…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.…”