Semi-metals as potential thermoelectric materials

Abstract

The best thermoelectric materials are believed to be heavily doped semiconductors. The presence of a band gap is assumed to be essential to achieve large thermoelectric power factor and figure of merit. In this work, we propose semi-metals with large asymmetry between conduction and valence bands as an alternative class of thermoelectric materials. To illustrate the idea, we study semi-metallic HgTe in details experimentally and theoretically. We employ ab initio calculations with hybrid exchange-correlation functional to accurately describe the electronic band structure in conjunction with the Boltzmann Transport theory to investigate the electronic transport properties. We calculate the lattice thermal conductivity using first principles calculations and evaluate the overall figure of merit. To validate our theoretical approach, we prepare semi-metallic HgTe samples and characterize their transport properties. Our first-principles calculations agree well with the experimental data. We show that intrinsic HgTe, a semimetal with large disparity in its electron and hole masses, has a high thermoelectric power factor that is comparable to the best known thermoelectric materials. Finally, we propose other possible materials with similar band structures as potential candidates for thermoelectric applications.

Largely Suppressed Magneto-Thermal Conductivity and Enhanced Magneto-Thermoelectric Properties in PtSn 4

“…We then investigated the possible effect of the thermal contact resistances and demonstrated the need for careful contact preparation. After careful contact preparation, as described above, we investigated samples 6 Research with lengths ranging from 4.5 to 7 mm, but similar crosssections and contact areas. We obtained consistent results for all the samples at any magnetic field or temperature investigated, and therefore did not observe any indication of diminished thermal conductivity owing to contact.…”

“…Therefore, semimetals with symmetric conduction and valence bands have generally been viewed as poor thermoelectric materials. One way to overcome this disadvantage is to look for semimetals with a large asymmetry between the conduction and valence bands, where the large disparity in their electron and hole effective masses could ensure a sizable S [6,7]. Another recently proposed method of generating a large thermopower in topological Dirac/Weyl semimetals is to apply a sufficiently large magnetic field, under which the thermopower will grow linearly without saturation [8].…”

Thermoelectric Properties of Novel Semimetals: A Case Study of YbMnSb2

“…To further demonstrate the potential of the unique band structure in YbMnSb 2 for thermoelectrics, we compare the thermopower (|α|) and power factor of YbMnSb 2 to other topological semimetals, including HgTe, [ 32 ] TaAs, [ 33 ] NbP, [ 34,35 ] Cd 3 As 2 , [ 36,37 ] ZrSiS, [ 38,39 ] Co 3 Sn 2 S 2 , [ 40 ] as well as the good thermoelectric semiconductors, for example, Bi 2 Te 3 , [ 41 ] Mg 3 Sb 2 , [ 42 ] and Yb 14 MnSb 11 , [ 43 ] as shown in Figure 3d. Generally, topological semimetals show a smaller |α| than that of thermoelectric semiconductors.…”

“…d) Comparison of thermopower and power factor of several topological semimetals to high-performance thermoelectric semiconductors at 300 K. To avoid the influence of other mechanisms, all the data are taken from single crystals without further doping or alloying. [29][30][31][32][33][34][35][36][37][38][39][40] state-of-the-art Bi 2 Te 3 thermoelectric material which has υ s of 2147 and 2070 m s −1 , along the ab-plane and the c-axis, respectively. [54] This low value of sound velocity, which is generally related to the weak chemical bonding, is one of the reasons leading to the intrinsically low lattice thermal conductivity of YbMnSb 2 .…”

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

“…where T is the temperature, S is the Seebeck coefficient (thermoelectric power), σ is the electrical conductivity, and κ L + κ e is the total thermal conductivity, consisting of lattice (κ L ) and electronic (κ e ) contributions. [10][11][12] However, currently available thermoelectric devices do not satisfy this requirement: for commercial applications, a conversion efficiency of at least 15% is needed (ZT > 1). 6 Such values may be attained by devices based on a variety of different thermoelectric materials, but in general only at high temperatures.…”