Enhanced Thermoelectric Properties in p‐Type Double Half‐Heusler Ti_2−yHf_yFeNiSb_2−xSn_x Compounds

Abstract

Double half‐Heusler Ti2FeNiSb2‐based compounds, which can be regarded as a combination of 17‐electron TiFeSb and 19‐electron TiNiSb, have a lower intrinsic thermal conductivity due to the smaller group velocity phonons and the disordered scattering by Fe/Ni. An enhanced room‐temperature Hall carrier concentration of ≈4.8 × 1021 cm−3 is achieved by doping Sn on the Sb site in a series of Ti2FeNiSb2−xSnx (x = 0.2, 0.3, 0.4, and 0.5) samples. Combined with the further decreased lattice thermal conductivity by alloying with Hf2FeNiSb2, a low lattice thermal conductivity of ≈1.95 W m−1 K−1 and a peak thermoelectric figure of merit (ZT) of ≈0.52 at 923 K are obtained in Ti1.6Hf0.4FeNiSb1.7Sn0.3, indicating the promising applications of double half‐Heusler compounds.

Enhanced Thermoelectric Properties of Ti2FeNiSb2 Double Half‐Heusler Compound by Sn Doping

“…In contrast, κ L of Sn‐doped Ti 2 FeNiSb 2 were reduced from ≈8.74 W m −1 K −1 (Ti 2 FeNiSb 2 ) to ≈7.47 W m −1 K −1 at room temperature (Figure 3c). In addition, κ L decreased with increasing temperature, and the lowest κ L of ≈3.22 W m −1 K −1 was achieved in Ti 2 FeNiSb 1.8 Sn 0.2 at 973 K. It is noted that the κ L of Ti 2 FeNiSb 1.8 Sn 0.2 is comparable to that of Ti 2 FeNiSb 2 with heavy Hf alloying, [ 17,20,21 ] indicating a potential for developing high‐performance DHH‐based TE compounds without rare elements. The reduction in the κ L of Sn‐doped samples is related to the intensified point defect phonon scattering by substitution of Sn at the Sb‐site based on the phonon scattering parameter ( Γ ) described as follows [ 22 ] where x is the doping fraction, Δ M / M is the rate of change of the atomic mass, ε is the elastic property, and a disorder and a pure are the lattice constants of disordered and pure alloys, respectively.…”

Advances in half-Heusler alloys for thermoelectric power generation

“…210 Some unusual points emerged, such as the large reduction in κ l just above and below x = 0.5 and massive apparent m DoS * values up to 23.8 m e, which was later confirmed by a separate group. 211 The emergence of defective HH phases and double-HH phases has provided an extended range of potential compositions to explore, which has allowed for the application of computational screening, beyond the common style of reporting the first principles properties of single phase HHs. 112,212 The emergence of these phases coincide with the development of effective band structure techniques, that allow supercell bandstructures to be compared to stoichiometric parent phases.…”

Metallic n‐Type Mg3Sb2 Single Crystals Demonstrate the Absence of Ionized Impurity Scattering and Enhanced Thermoelectric Performance

“…Near room temperature, the zT is significantly higher in the single crystal compared to that of polycrystalline Mg 3 Sb 2 . [ 2,39 ] Since the difference in the thermal conductivity is relatively small, the improvement of zT is mainly attributed to the removal of grain‐boundary electrical resistance. With increasing temperature, the effect of the grain boundaries gradually diminishes, and the zT values of the single crystal and polycrystalline samples start to converge.…”

“…a) Thermal conductivity and b) the zT of Te‐doped Mg 3 Sb 2 single crystal as a function of temperature. The zT for single crystals are substantially larger than that of polycrystalline samples [ 2,39 ] because of the removal of grain boundary resistance, especially at room temperature. The large measurement uncertainty in the thermal conductivity of single crystal, as indicated in the light red region, is likely due to the small size and irregular shape of the crystal.…”