High Efficiency Half‐Heusler Thermoelectric Materials for Energy Harvesting

Abstract

respectively the temperature of the hot side and cold side, Δ T = T H -T C and T avg are the temperature gradient and average between hot and cold sides. [ 4 ] The fi gure of merit zT is defi ned as zT = α 2 σT /( κ e + κ L ), where α , σ , T , κ e and κ L are respectively the Seebeck coeffi cient, the electrical conductivity, the absolute temperature, and the electrical and lattice components of total thermal conductivity κ . [ 2 ] High conversion effi ciency of 15%-20% is thought of as the "Holy Grail" for large scale application of TE technologies. [ 5 ] As depicted in Figure 1 , this conversion efficiency can be realized by using middle temperature (500-900 K) TE materials with very high zT or high temperature (>900 K) TE materials with compromised zT . Recently, much progress has been made in developing high effi ciency middle temperature TE materials: high zT 's of ≈1.5 at 750 K for n-type and ≈2.0 at for p-type have been achieved in PbTe-based alloys, [6][7][8][9] while n-type and p-type fi lled skutterudites have the maximum zT 's of ≈1.7 and ≈1.0, respectively, near 800 K. [ 10,11 ] Some other TE materials made of earth-abundant and non-toxic elements have also been identifi ed, such as single crystal SnSe ( zT ≈ 2.6 at 923 K), [ 12 ] silicides [ 13,14 ] and α -MgAgSb. [ 15 ] However, there remain tremendous challenges for most of these TE materials for large scale commercial application, mainly due to their relatively poor thermal stability and weak mechanical strength at high temperatures. In Half-Heusler (HH) compounds have gained ever-increasing popularity as promising high temperature thermoelectric materials. High fi gure of merit zT of ≈1.0 above 1000 K has recently been realized for both n-type and p-type HH compounds, demonstrating the realistic prospect of these high temperature compounds for high effi ciency power generation. Here, recent progress in advanced fabrication techniques and the intrinsic atomic disorders in HH compounds, which are linked to the understanding of the electrical transport, is discussed. Thermoelectric transport features of n-type ZrNiSn-based HH alloys are particularly emphasized, which is benefi cial to further improving thermoelectric performance and comprehensively understanding the underlying mechanisms in HH thermoelectric materials. The rational design and realization of new high performance p-type Fe(V,Nb)Sb-based HH compounds are also demonstrated. The outlook for future research directions of HH thermoelectric materials is also discussed.

Valleytronics in thermoelectric materials

“…(2) and shown by both experiments [106][107][108] and theory. 11,31 The study on p-type (V,Nb) FeSb-based materials, a kind of HH alloys with excellent TE performance in the high temperature range (T > 1000 K), 44,109 serves as a good example. 106 DFT calculations show that VFeSb possesses a flatter valence band than that of NbFeSb.…”

Magnetoelectric interaction and transport behaviours in magnetic nanocomposite thermoelectric materials

“…Where T, α, σ, κ E and κ L are the absolute temperature, Seebeck coefficient, electrical conductivity, and the electronic and lattice components of the thermal conductivity (κ), respectively. To optimize the thermal properties, various phonon engineering approaches were used to enhance phonon scattering and decrease κ L by having taken advantage of nanoinclusion [3][4][5][6][7][8][9][10][11][12][13] . A series of band structure engineering approaches were employed to improve the electrical properties [14][15][16][17][18][19][20] .…”

Attaining high mid-temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization

“…It is useful to compare the optimal operation temperature ('service temperature') of state-of-the-art TE materials and the temperature range in which most of the waste heat is produced. State-of-the-art TE materials have their best zT values (those between 1 and 2) in different temperature regimes; for example, Bi 2 Te 3 works best near room temperature, 3,4 whereas PbTe, Mg 2 Si 1-x Sn x , Half-Heusler compounds and filled skutterudites generally reach their best performance above 600 K. [5][6][7][8][9][10][11][12][13][14] There is a conspicuous lack of high-performance TE materials between 400 and 600 K, the mid-temperature range. Meanwhile, most of the waste heat produced (including various industrial sectors and automobile exhausts) is in the temperature range of 400-900 K, and hence it is unharvested.…”