Huge power factor in p-type half-Heusler alloys NbFeSb and TaFeSb

Abstract

NbFeSb is a promising thermoelectric material which according to experimental and theoretical studies exhibits a high power factor of up to 10 mW m −1 K −2 at room temperature and ZT of 1 at 1000 K. In all previous theoretical studies, κ latt is calculated using simplified models, which ignore structural defects. In this work, we calculate κ latt by solving the Boltzmann transport equation and subsequently including the contributions of grain boundaries, point defects and electron-phonon interaction. The results for κ latt and ZT are in excellent agreement with experimental measurements. In addition, we investigate theoretically the thermoelectric properties of TaFeSb. The material has recently been synthesised experimentally, thus confirming the theoretical hypothesis for its stability. This encourages a full-scale computation of its thermoelectric performance. Our results show that TaFeSb is indeed an excellent thermoelectric material which has a very high power factor of 16 mW m −1 K −2 at room temperature and ZT of 1.5 at 1000 K.

First‐principles calculations to investigate structural stabilities, mechanical and optoelectronic properties of NbCoSn and NbFeSb half‐Heusler compounds

“…The values of the energy band‐gap within both schemes for NbCoSn and NbFeSb HH compounds are shown in Table 3. Our gap values are in good agreement with those of Xi et al [47] (VASP code) for NbCoSn, and He et al [48] (QE and ELK codes), Joshi et al [36] (QE code), Naydenov et al [16] (CASTEP code) for NbFeSb with GGA approximation, by contrast the values of energy band‐gap of GGA + U are higher which is due to the electron correlation effects by using the Hubbard potential. The total and partial densities of states (DOSs) were also analyzed to understand the contribution and distribution of the electrons of the constituent atoms in the bands (Figure 7).…”

“…1.004 (GGA) 0.514 (GGA) 0.958 (GGA + U) 0.955 (GGA + U) 0.987 [47] 0.51 [48], 0.52 [36], 0.53 [16] Note: Only the theoretical available results are shown in the table.…”

“…The HH semiconductors NbCoSn and NbFeSb compounds are known as the potential thermoelectric material due to their large power factor and thermal conductivity [16, 17]. Other such HH semiconductors are CoTiSb, CoZrSb, FeVSb and NiTiSn [18–20].…”

Advances in half-Heusler alloys for thermoelectric power generation

“…Some publications also make use of the simplified Slack model. 104,106 While work on calculating κ l from the phonon bandstructure exists, [107][108][109][110][111][112][113] it is more typical to use approximations based on calculated elastic properties or experimental acoustic properties to 10 estimate v s , θ D and τ ph . The most fundamental description of τ ph considers Umklapp scattering, which can be written as: 105 1 = 2 2 GV 0 ω 2 (Eqn.…”

First-Principles Investigation of Thermoelectric Properties of Half-Heusler Alloy NbFeTe

“…The phonon scattering is controlled by Umklapp processes at high temperatures, such that κ L is inversely proportional to T. The values of κ L computed using both methods are in good conformity with each other. κ L of NbFeTe is smaller than of NbFeSb (experimental value = 17.7 W/mK at 300 K, 22.0 W/mK at 300 K (using Slack's equation)) in the entire range of temperature [30][31][32][33]. The values of κ L for NbFeTe calculated using the Slack's equation and the Callaway's model at 300 K are listed in Table 3.…”