Functional Graded Germanium–Lead Chalcogenide‐Based Thermoelectric Module for Renewable Energy Applications

Abstract

methods to enhance the materials' thermoelectric properties, practical design considerations including geometrical optimization and minimization of contact resistances and long-term properties degradation should be considered. For many years, thermoelectric power generation has enjoyed its greatest success in special and exotic applications, such as the space missions, in which the chalcogenides class of thermoelectric materials (e.g., GeTe, [1][2][3][4] PbTe, [5][6][7][8][9][10] PbS, [11][12][13][14] SnTe, [15][16][17][18][19][20][21] or their alloys) is the most thermoelectrically effi cient in the intermediate temperature range of ≈500 °C, but still the system conversion effi ciency for a state-ofpractice NASA RTG (radioisotope thermoelectric generator) is about 6%, [ 22 ] where in this type of application environmental issues and cost are not the main concerns. In this thermoelectric materials class, it was recently reported that upon proper compositional investigation for systems exhibiting a miscibility gap between two individual chalcogenide components, sub-micron thermodynamic-driven phase separation features are expected, leading to dramatically reduced thermal conductivity values and enhanced ZT s. Two examples are the p-type Ge 0.87 Pb 0.13 Te, [ 1 ] shown in Figure 1 a, and the n-type 0.055% PbI 2 doped (PbSn 0.05 Te) 0.92 (PbS) 0.08 [ 11 ] compositions, exhibiting very high maximal ZT s of ≈2.2 and ≈1.5, respectively, and correspondingly a very high thermoelectric potential.For the latter, investigation of the PbS-PbTe quasi-binary phase diagram, Figure 1 b reveals an extended miscibility gap at temperatures below 800 °C (1073 K in Figure 1 b), in which a higher-temperature solution-treated single phase (the upper scanning electron microscopy, SEM image) is expected to follow a rapid phase separation to two individual PbTe-and PbS-rich phases (the lower SEM image) by either the spinodal decomposition or nucleation and growth mechanisms, upon cooling, depending on the specifi c composition. Due to the rapid nature of these phase separation reactions, the apparent alternating phases are usually fi nely dispersed, making them very useful phonon scattering centers for thermal conductivity reduction. Due to its thermodynamic origin, such a submicron phase generation is considered much more stable at elevated operating temperatures, compared to any other mechanical nano-features generation approaches such as ball-milling, which are expected to follow coarsening into the micron scale with long-term operations.

Study on the High Temperature Interfacial Stability of Ti/Mo/Yb0.3Co4Sb12 Thermoelectric Joints

“…Among the investigated various systems of TE materials, silicides [6][7][8][9], half-heuslers [10,11], and tellurides (e.g., of Bi [12][13][14], Pb [15][16][17][18] and Ge [19,20]) have been widely studied and some have been practically applied in TEGs. Besides, a number of materials featuring excellent TE properties (high ZT value) and a relatively lower cost, low toxicity, and good mechanical properties, such as filled skutterudite (SKD), also attract extensive attention and have been actively pursued for being converted into TEGs [21][22][23][24][25][26].…”

Compatibility between Co-Metallized PbTe Thermoelectric Legs and an Ag–Cu–In Brazing Alloy

“…p -type Bi x Sb 2- x Te 3 [1,2,3,4,5,6] and n -type Bi 2 Te 3- x Se x [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. At the intermediate 300–500 °C temperature range, PbTe-based compositions are the most thermoelectrically efficient [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33], where a very interesting, highly explored composition is the n -type 9.104 × 10 −3 mol % PbI 2 -doped PbTe [34,35,36,37,38]. …”

Material Optimization for a High Power Thermoelectric Generator in Wearable Applications

“…Many efforts have been made toward enhancing the figure of merit (ZT) values in several existing TE material classes for applications in varied temperature ranges, including silicides [6], half-Heuslers [7,8], and tellurides (e.g., of Bi [9], Pb [10,11] and Ge [12,13]). On the other hand, from the Appl.…”