![]() Consequently, the bandgaps are essentially the same for XNiSn (X = Ti, Zr, or Hf) with different cations. In principle, the value of the bandgap for HH compound XYZ largely depends on the bond strength between Y and Z, which means the Pauling electronegativities of Y and Z determine the bandgap ( E g). As a consequence, the peak value of zT = 0.79 has been achieved in LiCd 0.98Ag 0.02Sb at 633 K. ![]() Furthermore, Ag doping can effectively enhance the power factor to 21.35 μW cm −1 K −2 at 393 K via carrier concentration optimization and multiple electronic valence bands contribution. Meanwhile, both vibration modes of Li and weak chemical bonding between Cd and Sb result in low lattice thermal conductivity despite small mean atomic mass of LiCdSb. The high-symmetry cubic structure and covalent interactions guarantee high power factor. Li ions occupy the large octahedral voids as Zintl cations to donate electrons, while Cd and Sb covalently connect to form a zinc blende–sublattice as polyanionic framework. In this work, we rationally construct a HH lattice based on the composition of LiCdSb for the TE consideration using Zintl chemistry ( Figure 1). The coexistence of covalent bonds and ionic bonds yields large anharmonicity, resulting in suppressed lattice thermal conductivity. Zintl phase compounds usually exhibit low thermal conductivity as a result of complex crystal structure and chemical bonding. However, unearthing HH compounds with intrinsically low thermal conductivity is still a blinking area needed to investigate and explore. ![]() In this situation, the target for lowering the thermal conductivity has been established, which involves multidimensional defects including solid solution, doping, grain boundary, and nanostructure to scatter phonons. In comparison with other classic TE systems such as PbTe, Bi 2Te 3, SnSe, BiCuSeO, and Zintls, the high thermal conductivity of HH compounds largely impedes the further enhancement of TE properties, which is determined by the dimensionless figure of merit zT = ( σS 2/ κ) T, where S is Seebeck coefficient, σ is electrical conductivity, T is the absolute temperature, and κ is total thermal conductivity including lattice thermal conductivity ( κ L) and carrier thermal conductivity ( κ C). These works demonstrate the reliable aspect of HH compounds and pave the way for TE commercialization. synthesized n-type (Hf 0.6Zr 0.4)NiSn 0.99Sb 0.01 sample to build a TE generator, which exhibits high power density of 13.93 W cm −2 and conversion efficiency of 10.7% under Δ T = 674 K. Subsequently, they assembled a single-stage TE module with 8 n–p HH couples with p-type (Nb 0.8Ta 0.2) 0.8Ti 0.2FeSb and n-type Hf 0.5Zr 0.5NiSn 0.98Sb 0.02 to achieve a high conversion efficiency of 8.3% and high power density of 2.11 W cm −2 when hot and cold side temperatures are 997 and 342 K, respectively. utilized p-type FeNbSb material and realized a high conversion efficiency of 6.2% and a high power density of 2.2 W cm −2 at a temperature difference of 655 K in an eight-couple prototype TE module. Herein, it is demonstrated that the half-Heusler compound LiCdSb is a competitive thermoelectric parent, and low thermal conductivity can indeed be realized in half-Heusler compounds through Zintl chemistry.ĭue to their low cost, high chemical stability, excellent electrical transport, and mechanical properties, half-Heusler (HH) compounds have been one indispensable class of thermoelectric (TE) materials for energy harvesting over the last two decades. In view of the low thermal conductivity, the figure of merit zT reaches 0.79 at 633 K. As a result, a high power factor up to 21.35 μW cm −1 K −2 at 393 K is achieved in LiCd 0.94Ag 0.06Sb. Ag doping is further conducted for boosting the electronic quality factor B E from 2.5 to 5.2 μW cm −1 K −2 due to the energy band modulation. ![]() The weak bonding within the polyanions combined with the resonance vibration modes of Li + contributes to the small lattice thermal conductivity of pristine LiCdSb as low as 3.2 W m −1 K −1 at 303 K and 0.85 W m −1 K −1 at 573 K. Herein, from the perspective of material design, a new half-Heusler lattice with low lattice thermal conductivity by using Zintl chemistry based on the composition of LiCdSb is rationally constructed. Half-Heusler compounds usually possess ultrahigh power factors, while the large thermal conductivity hinders the further optimization of their thermoelectric properties.
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