Large Enhancements in the Thermoelectric Power Factor of Bulk PbTe at High Temperature by Synergistic Nanostructuring

Abstract

Thermoelectric heat-to-electrical-energy converters will play a role in energy management if efficient, stable, and inexpensive materials can be developed. Research to increase the figure of merit ZT is focused on a variety of novel thermoelectric materials and approaches. [1][2][3][4][5][6][7][8][9] Significant advances have come in recent years from the development of nanostructured semiconductors both in thin-film [10] and bulk form. [11][12][13][14] In the thin films, values ZT > 3 have been claimed for PbTe/PbSe superlattice structures, [15] while values of 1.5-1.7 at 700 K have been reported for AgPb 18 SbTe 20, [12] NaPb 20 SbTe 22 , [16] PbTe-PbS, [17] and Tl-PbTe. [18] This progress promises to impact several energy-conversion applications. The advancements have primarily come from sizeable reductions in thermal conductivity, which is largely the result of the scattering of mid-and long-wavelength phonons at the interfaces of the nanoscale inclusions at high temperature. [18,19] Although further increases in ZT can be anticipated by additional reduction of the thermal conductivity, a lower limit is expected to be reached. Thus, dramatic enhancements in ZT can only come from spectacular increases in the power factor (S 2 s). This problem is harder to tackle, since standard charge-transport theory does not offer specific guidance on how to dramatically increase the power factor. Its solution will require breakthroughs in the understanding and control of charge-transport mechanisms in complex materials. An important factor affecting charge transport (e.g. mobility m = et/m, where m is the carrier effective mass) and thus power factor in solids is the relaxation time t, which has an energy dependence [Eq. (1), where E is the energy and r is ascattering parameter]. [20] This relationship implies that the energy dependence of t impacts the mobility, electrical conductivity (s = N em, N = carrier concentration), and thermopower in semiconductors, especially for large values of r owing to their dependence on the relaxation time. In PbTe it is not possible to cause significant changes in the scattering mechanism by making solid solutions or through carrier doping.[21] A more fundamental question is whether the relative contributions of known scattering mechanisms, or even the actual mechanisms themselves in PbTe, can be altered through nanostructuring. For example, can features buried on the nanoscale fundamentally change the electronic structure and therefore charge transport?We report herein a new way to achieve dramatic changes in the carrier transport in PbTe, which leads to large increases in the thermoelectric power factor (S 2 s) at high temperatures. We observe the enhancements only when PbTe is co-nanostructured with two different phases. We show that when lead and antimony are present simultaneously as nanodots throughout the matrix of PbTe, the conductivity behavior becomes novel. We observe unprecedented temperature dependence that is a complicated function of the Pb/Sb ratio. The most important conse...

Enhanced thermoelectric performance of a new half-Heusler derivative Zr9Ni7Sn8 bulk nanocomposite: enhanced electrical conductivity and low thermal conductivity

“…The best possible strategy for increasing ZT is to decouple the thermoelectric parameters; a, s and k by doping, solid solution alloying and nanostructuring approaches. These concepts have been demonstrated theoretically and experimentally in several systems, such as, Bi 2 Te 3 , [2][3][4][5][6] AgPb m SbTe 2+m (LAST), 7 TeAgGeSb, 8 PbTe, 9 …”

High-performance nanostructured thermoelectric materials

“…Obvious ZT improvements have been obtained in (Zr,Hf )NiSn half-Heusler alloys by adding nano-ZrO 2 [36], in Bi 2 Te 3 by adding nano-SiC particles [37], and in Yb y Co 4 Sb 12 by dispersing in situ partially oxidized Yb 2 O 3 nanoparticles [38]. It is also reported that more signifi cant enhancements can be achieved by embedding metal or conductive nanoparticles into a TE material matrix: examples include lead and antimony in PbTe [39], antimony in Yb y Co 4 Sb 12 [40], and ErAs in In 0.53 Ga 0.47 As [41]. Th is kind of nanoscale dispersed phase can be located at the grain boundary or within the grains.…”

Phase stability of ScN-based solid solutions for thermoelectric applications from first-principles calculations

“…9 These power factors are comparable to state of the art thermoelectric material such as pure Bi 2 Te 3 or PbTe. [10][11][12] The value is high considering that it is obtained for a nitride material without any deliberate optimization of doping and has been suggested to be related to electronic structure effects of nitrogen vacancies and oxygen incorporation. 9,13 However, for most practical applications, the thermoelectric figure of merit (ZT) of ScN is too low.…”