Two-Dimensional β-PdX₂ (X=S, Se, and Te) Monolayers with Promising Potential for Thermoelectric Applications

Abstract

Transition metal dichalcogenides have attracted extensive research attention due to their unique electronic, topological, and optical properties. Based on first-principles methods and Boltzmann transport theory, the thermoelectric performance of β-PdX 2 (X = S, Se, and Te) monolayers was comprehensively studied in this work. It is worth noting that the structural anisotropy of β-PdX 2 monolayers leads to obvious anisotropy of thermoelectric coefficients along the x and y directions. By investigating the thermal transport up to fourphonon scattering, it was found that the strong higher-order phonon scattering plays a decisive role in ultra-low lattice thermal conductivity of β-PdX 2 monolayers. A low lattice thermal conductivity of 3.4 (1.0) W m −1 K −1 is predicted for β-PdTe 2 at 300 K along the x (y) direction. In addition, due to the suitable band gap and high carrier mobility, the highest power factor of 25.7 mW m −1 K −2 is obtained in n-type β-PdX 2 monolayers, which is superior to many other two-dimensional thermoelectric materials. Finally, a maximum ZT of 5.2 is achieved for the n-type β-PdS 2 monolayer along the y direction at 600 K. Meanwhile, the maximum p-type ZT also reaches 3.3 along the y direction at 600 K in the β-PdSe 2 monolayer. Our results demonstrate that β-PdX 2 monolayers are promising candidates for two-dimensional thermoelectric materials with excellent conversion performance.

Theoretical determination of superior high-temperature thermoelectricity in an n-type doped 2H-ZrI2 monolayer

“…After covering the 4ph scattering, the κ L value is reduced only from 20.30/6.69 to 19.12/5.77 W m −1 K −1 at 300/ 900 K, leading to a slightly overestimated figure of merit from 1.33/3.57 to 1.38/3.74 for the n-type doped 2H-ZrI 2 monolayer. These results confirm that the 4ph scattering can be simply considered as a high-order perturbation in the 2H-ZrI 2 monolayer, quite different from some other 2D TE materials where a strong 4ph scattering gives rise to around a 60-80% reduction of the κ L value at 300 K. 39,60,61 To better elucidate the underlying mechanism of phonon heat transport in 2H-ZrI 2 , we performed the calculation of phonon group velocity by |v λ (k)| = dω λ (k)/dk. As shown in Fig.…”

“…Such a high zT value in our n-type doped system is far superior to those of the well-known 2H-TMDC monolayers, [24][25][26] and is comparable to those of other excellent TE materials such as monolayers Bi 2 O 2 Se (3.35 at 800 K), 22 α-In 2 Se 3 (3.02 at 400 K), 28 ZrGe 2 N 4 (3.93 at 1100 K), 31 and β-PdS 2 (5.20 at 700 K). 39 The largest zT in the presence of the bipolar effect even reaches 7.86 at 700 K in the p-type 1T′-ZrI 2 monolayer. 36 Overall, our calculations indicate that 2H-ZrI 2 can be a promising n-type TE material through a moderate adjustment of the electron concentration, especially in a high-temperature environment.…”

“…Among a plethora of 2D potential TE materials, only a few candidates have been predicted to show a high efficiency ( zT > 3) by optimal carrier doping at different specific temperatures, in which an inherent (ultra)low lattice thermal conductivity often plays a crucial role. 27–39…”

“…Among a plethora of 2D potential TE materials, only a few candidates have been predicted to show a high efficiency (zT > 3) by optimal carrier doping at different specific temperatures, in which an inherent (ultra)low lattice thermal conductivity often plays a crucial role. [27][28][29][30][31][32][33][34][35][36][37][38][39] Most recently, monolayer 2H-ZrI 2 has been recognized as a promising candidate for potential applications in spintronics and valleytronics. 40 It has been shown that the manipulation of the valley degree of freedom can be used not only to process information for highly efficient semiconducting nanodevices, 41 but also to engineer the band structure for better TE performance.…”

High thermoelectric performance of TlInSe3 with ultra-low lattice thermal conductivity

“…San-Dong Guo, Xi'an University of Posts and Telecommunications, China by Dutta, displaying its intrinsic ultra-low k l of 0.62-0.4 W/mK [10]. However, the ZT of bulk Tl compounds (ZT value of TlInTe 2 is 1.78, Tl 9 BiTe 6 is about 1, and Tl 4 ZrTe 4 is only 0.16) is low compared to other TE materials because of the low power factor (PF) [7,[13][14][15][16][17][18][19]. Therefore, an ultra-low k l and a high PF is necessary to obtain a high ZT value.…”