First-Principles Investigation on the Significant Anisotropic Thermoelectric Transport Performance of a Hf₂Cl₄ Monolayer

Abstract

Recently, a series of novel thermoelectric (TE) materials have been rapidly screened out through high-throughput calculation; meanwhile, although this method improves the screening speed, it also reduces the accuracy of estimation. Therefore, further accurate analysis of the newly reported materials' electrical and thermal transport properties should be conducted to understand their microscopic transport mechanism. In this work, we investigate the TE transport properties of monolayer Hf 2 Cl 4 in which it has been figured out that there exists a high electronic fitness function (EFF) value for TE applications based on the first-principles approach by using density functional theory and the semiclassical Boltzmann transport equation. The TE parameters of monolayer Hf 2 Cl 4 , including thermal conductivity, Seebeck coefficient, electrical conductivity, and so on, are calculated to evaluate its figure of merit ZT at temperatures of 300, 500, and 700 K. It is found that these TE parameters are highly anisotropic between x-and y-directions, which is the critical factor for its excellent TE performance. The optimal figure of merit of 3.2 is achieved along the x-direction for hole doping at 700 K. Our study reveals that monolayer Hf 2 Cl 4 could be a suitable candidate for TE materials, and high-throughput calculation screening is effective for enhancing TE performance.

Monolayer Sc2I2S2: An Excellent n-Type Thermoelectric Material with Significant Anisotropy

“…In addition, the relaxation time of <2 THz phonons is about 1−100 ps, as shown in Figure 6f. This value is comparable with those of previously reported low κ l materials, such as Al 2 I 2 Se 2 (1−10 2 ps), 61 SnP 3 (<10 2 ps), 66 and GeSe (<10 2 ps) 67 monolayers, corresponding to κ l values of 0.29−0.70, 0.48, and 3.58 W/mK at 300 K. Thus, it has a strong three-phonon scattering process, resulting in a small κ l . At the same time, in Figure 6c,d, the highest phonon v g for acoustic branches is about ∼4.5 km/s, much lower than those of TiNF (∼9.0 km/s), 37 TiNCl (∼8.0 km/s), 37 and TiNBr (∼6.5 km/s) 37 monolayers, corresponding with the κ l of 30.30 (13.42), 26.74 (15.69), and 20.23 (13.05)W/mK along the x-direction (y-direction) at 300 K. Therefore, the low phonon v g and τ qs of monolayer Sc 2 I 2 S 2 result in the low κ l and thus suggest that this material can be a potential thermoelectric material.…”

“…The phonon–phonon scattering becomes stronger with an increased temperature, leading to a decrease in the κ l of the material. , The results show that Sc 2 I 2 S 2 has a low κ l in both directions, especially the κ l which is 2.41 W/mK at 700 K in the x -direction, and the κ l is 3.33 W/mK at 700 K in the y -direction. The κ l of Sc 2 I 2 S 2 is lower than the reported κ l of Hf 2 Cl 4 , an excellent thermoelectric material . The main reason for this low κ l will be discussed by the phonon mode next.…”

“…The κ l of Sc 2 I 2 S 2 is lower than the reported κ l of Hf 2 Cl 4 , an excellent thermoelectric material. 61 The main reason for this low κ l will be discussed by the phonon mode next. Figure 6c,d reflects the relationship between the phonon group velocity (v g ) for different directions.…”

Theoretical Prediction of the Monolayer Hf2Br4 as Promising Thermoelectric Material

“…For ple, the 𝑘 𝑙 is 10.91 W/mK and 6.47 W/mK along the a-axis and b-axis at 300 K, r tively. The 𝑘 𝑙 of monolayer Hf2Br4 is lower than that of the reported analog mon Hf2Cl4 [36]. To further explore the physical insights of the thermal transport for the olayer Hf2Br4, a further mode level analysis was performed.…”

Lower thermal conductivity of body centered cubic carbon (C14): a comparative study with diamond

“…Carbon materials had been well known to display various kinds of superior properties, making them suitable for designing conductive devices, [1][2][3][4][5][6][7][8][9] especially decorated with suitable transition-metal based or oxygen-containing clusters. [10][11][12][13][14][15][16][17][18][19][20] The special electronic structure of carbon atoms enables them to form all kinds of crystal structures via different hybrid bonding states, like sp 3 , sp 2 , and sp. Within the last few decades, a variety of carbon allotropes, like diamond, graphene, carbon nanotubes, and fullerenes, had been successfully synthesized, and due to their specific functionalities and structural features, they had been applied as important preparation materials.…”