Mechanical and physical properties of alloys and metals

Challenges and Progress in Contact Development for PbTe‐based Thermoelectrics

“…The CTE of Co (~12.5 × 10 À 6 K À 1 at 273-373 K [89] ) is significantly smaller than that of PbTe. However, low values of 1 c between PbTe and Co-based contact layers have been measured, for example, ~21 × 10 À 10 Ω m 2 -22 × 10 À 10 Ω m 2 undoped PbTe-based legs, [57] ~30 × 10 À 10 Ω m 2 in n-type PbTe doped with 9.104 mmol% PbI 2 -based legs, [55] ~27 × 10 À 10 Ω m 2 -28 × 10 À 10 Ω m 2 in p-type Pb 0.6 Sn 0.4 Te-based legs.…”

“…[40] The P of the module operating at T h ~700 K was reduced by ~19% over ~9 months and failed after ~15 months. [39] AlÀ Te based secondary phases were observed at the Al/p-type PbTe interface in the module following failure after ~15 month operation at ~700 K. [39] The CTE of metallic Ag (~18.7 × 10 À 6 K À 1 at 273 K-373 K [89] ) is well-matched with that of PbTe. After bonding Ag to undoped PbTe at 823 K for 3 h, no impurity phases have been observed at the interface.…”

“…[72] The amount of formed secondary phases was greatly increased during annealing at 823 K for undoped PbTe. [72] This is supported by phase diagram analysis of the PbTeÀ Ag system, which shows an equilibrium of PbTe and Ag [96] (and Ag 2 Te [97,98] ) up to 833 K. [96] In the case of p-type Pb 0.6 Sn 0.4 Te, the secondary phases such as Ag 4 Sn and Ag 2 Te were formed at the interface with between Ag and p-type Pb 0.6 Sn 0.4 Te after co-sintering at 823 K. [68] The CTE of metallic Cu (~17.0 × 10 À 6 K À 1 at 273 K-373 K [89] ) matches that of PbTe relatively well. After bonding Cu to undoped PbTe at 823 K for 3 h, no impurity phases have been observed at the interface.…”

“…[54] Similarly, no secondary phases were observed after co-sintering of n-type PbTe doped with 9.104 mmol% PbI 2 with Co disks at 993 K. [55] This is in good agreement with the phase diagram of the PbTeÀ Co vertical section, showing PbTe in equilibrium up to ~1073 K and negligibly low solubility of Co in PbTe. [100] Co 80 Fe 20 -based contact layers, whose CTE (~12.0 × 10 À 6 K À 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][59][60][61] Values for 1 c between Co 80 Fe 20 and p-type PbTe 0.973 Na 0.02 Ge 0.007 Te (~8 × 10 À 10 Ω m 2 -20 × 10 À 10 Ω m 2 ), [17] ntype PbTe 0.98 Ga 0.02 Te (~7 × 10 À 10 Ω m 2 -29 × 10 À 10 Ω m 2 ), [17] and n-type Pb 0.98 Ga 0.02 Te doped with 3 at.% GeTe (� 10 × 10 À 10 Ω m 2 ) [61] are comparable to PbTe/Co contacts.…”

“…[78] Hot side contacts made of stainless steel have also been used in place of Fe in SNAP-21 (System for Nuclear Auxiliary Power) RTGs developed for deep sea applications. [77] The CTE of the refractory metals Mo (~5.1 × 10 À 6 K À 1 at 273-373 K [89] ) and W (~4.5 × 10 À 6 K À 1 at 273-373 K [92] ) is significantly lower than that of PbTe. The 1 c between PbTe legs and W contact layers were ~24 × 10 À 10 Ω m 2 for p-type PbTe and ~18 × 10 À 10 Ω m 2 for n-type PbTe.…”