Stress-controlled thermoelectric module for energy harvesting and its application for the significant enhancement of the power factor of Bi₂Te₃-based thermoelectrics

Abstract

We propose a model of a thermoelectric module in which the performance parameters can be controlled by applied tuneable stress. This model includes a miniature high-pressure anvil-type cell and a specially designed thermoelectric module that is compressed between two opposite anvils. High thermally conductive high-pressure anvils that can be made, for instance, of sintered technical diamonds with enhanced thermal conductivity, would enable efficient heat absorption or rejection from a thermoelectric module. Using a high-pressure cell as a prototype of a stress-controlled thermoelectric converter, we investigated the effect of applied high pressure on the power factors of several single-crystalline thermoelectrics, including binary p-type Bi2Te3, and multi-component (Bi,Sb)2Te3 and Bi2(Te,Se,S)3 solid solutions. We found that a moderate applied pressure of a few GPa significantly enhances the power factors of some of these thermoelectrics. Thus, they might be more efficiently utilized in stress-controlled thermoelectric modules. In the example of one of these thermoelectrics crystallizing in the same rhombohedral structure, we examined the crystal lattice stability under moderate high pressures. We uncovered an abnormal compression of the rhombohedral lattice of (Bi0.25,Sb0.75)2Te3 along the c-axis in a hexagonal unit cell, and detected two phase transitions to the C2/m and C2/c monoclinic structures above 9.5 and 18 GPa, respectively.

Strategies and challenges of high-pressure methods applied to thermoelectric materials

“…4(c)]. 52,53 The thermopower curve of Sb 1.5 Bi 0.5 Te 3 (2) [ Fig. 4(c)] looks quite similar to that of heavily doped p-Bi 2 Te 3 (3) [ Fig.…”

“…However, this is a challenging requirement for high-pressure studies. To date, several different types of cells or setups combining electrical and thermoelectric measurements have been devised, [45][46][47][48][49][50][51][52][53] and techniques that enable measurements of all relevant thermoelectric properties under the same conditions have been recently developed. 4,5,[54][55][56] All of these methods have their merits and limitations, but in any case there is still a need for more refined and accurate techniques.…”

“…13,[67][68][69][70][71][72] For this reason, Bi 2 Te 3 and its solid solutions, (Bi,Sb) 2 (Te,Se,S) 3 have been the most widely investigated with regard to high-pressure transport. 23,42,[51][52][53][54]58,73,74 Bi 2 Te 3 , Sb 2 Te 3 , and (Bi,Sb) 2 Te 3 crystallize in the rhombohedral R3m structure (Fig. 1), and near 6-7 GPa or somewhat above they all undergo a phase transition to the monoclinic C2/m lattice.…”

“…1), and near 6-7 GPa or somewhat above they all undergo a phase transition to the monoclinic C2/m lattice. 30,53,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91] As shown by studies on high-quality single crystals of Bi 2 Te 3 , the pressure behavior of its Seebeck coefficient depends strongly on carrier concentration. 51,53 For example, in undoped p-type crystals with carrier concentrations of about 10 17 cm −3 and below, an applied pressure of 2-4 GPa induces a double p-n-p sign inversion [ p-Bi 2 Te 3 (1) in Fig.…”

“…(a) These dependences were measured on single-crystalline samples with carrier concentrations of p = 5 × 10 17 cm −3 in p-Bi 2 Te 3 (1), p = 3 × 10 18 cm −3 in p-Bi 2 Te 3 (2), p = 10 19 cm −3 in p-Bi 2 Te 3 (3), n = 10 18 cm −3 in n-Bi 2 Te 3 (1), n = 4 × 10 18 cm −3 in n-Bi 2 Te 3 (2), and n = 10 19 cm −3 in n-Bi 2 Te 3 (3). Data taken from Ovsyannikov et al, 52 Korobeinikov et al, 53 and Brazhkin et al 51 (b) Data taken from Polvani et al 58 and Meng et al [59][60][61] (c) Data taken from Ovsyannikov et al, 52 Brazhkin et al, 51 and Jacobsen et al 54 (d) Data taken from Ovsyannikov et al, 41 Jacobsen et al, 55 and Baker et al 5 (e) Data taken from Ovsyannikov et al, 62 Korobeinikov et al, 43 and Chen et al 63 (f ) Data taken from Meng et al, 65 Wu et al, 10 Morozova et al, 44 Baker et al, 56 Chen et al, 6 and Yu et al 64…”