High Thermoelectric Performance in 2D Technetium Dichalcogenides TcX₂ (X = S, Se, or Te)

Abstract

In recent years, the search for alternative energy sources has been of major research interest, and one of the potential solutions is thermoelectricity. Moreover, studies on the emergence of transition-metal dichalcogenides (TMDs) have been unstoppable because of their unique properties. Among this group of materials, technetium-based TMDs (TcX 2 , where X = S, Se, or Te) are one of the least investigated materials. Using first-principles calculations, we systematically studied the structural stability and electronic properties of bulk and monolayer TcX 2 in 1T dp (1T double prime), 1T′, 1T, and 2H crystal structures as well as the thermoelectric properties of the bulk and monolayer 1T dp phases. Formation energy calculations, phonon dispersion, and molecular dynamic simulation results revealed that only the 1T dp phase is stable, while 1T′, 1T, and 2H are unstable. These findings imply the possible synthesis of monolayer 1T dp -TcX 2 . With regard to the electronic properties under the hybrid functional approach, bulk 1T dp -TcTe 2 , TcSe 2 , and TcS 2 exhibit indirect band gaps of 0.37, 1.01, and 1.19 eV, respectively. For the monolayer phase, enlarged indirect band gaps of 1.21, 1.64, and 1.87 eV, respectively, were observed. Surprisingly, the calculated ZT numbers at 1200 K for monolayer TcTe 2 are 1.78 (p-type) and 1.84 (n-type), which are comparable to those of the currently synthesized excellent thermoelectric materials. Finally, the thermoelectric properties of TcTe 2 are significantly improved when reducing the dimensionality from bulk to monolayer at high temperatures. Our findings provide crucial evidence regarding the structural stability, robust electronic properties, and excellent thermoelectric properties in TcX 2 for potential optoelectronic and thermoelectric applications.

Nontrivial Topology in Monolayer MA2Z4 (M = Ti, Zr, or Hf; A = Si or Ge; and Z = N, P, As, Sb, or Bi)

“…Among them, graphene, which is renowned for its exceptional electronic properties such as high electron mobility and remarkable mechanical strength, is the first 2D material discovered to have a nontrivial topological phenomenon . Since graphene was obtained experimentally, thousands of new 2D materials have been proposed, − and many have been synthesized. − Beyond graphene, the other reported two-dimensional topological materials possessing honeycomb structures are III–V buckled honeycombs, , MXenes, − transition metal dichalcogenides (TMD), − Janus materials, , ternary transition metal chalcogenides, , functionalized Bi/Sb, arsenene oxide, and RuClBr . Additionally, other 2D topological compounds in different structures such as copper sulfide, Zintl compounds, , half-Heusler compounds, and ilmenite oxidizes also exist.…”

First-principles predictions of enhanced thermoelectric properties for Cs2SnI2Cl2 and Cs2PbI2Cl2 monolayers with spin–orbit coupling

“…These properties are crucial to the effective utilization and management of thermal energy as well as thermoelectrics [23]. Due to the quantum confinement effect, the decreased thermal conductivity and favorable electronic structure can be observed in some 2D systems, several studies have shown that the thermoelectric properties in monolayer materials are better than that of the corresponding bulk materials, such as TcTe 2 [24], CrSe 2 [25], α-PtO 2 [26] and so on. For the perovskites, bidimensionalization can improve the stability, the electronic structure characteristics, and thermoelectric transport properties, which is conducive to optimizing the thermoelectric performance by regulating the thermoelectric parameters.…”

Two-Dimensional AMgB (A = Na, K; B = P, As, Sb, Bi) with Promising Optoelectronic and Thermoelectric Performances

“…21 However, they found that SnS 2 nanosheets show a negative correlation between κ e and σ, indicating that the reduction in thickness can effectively improve its thermoelectric efficiency. Indeed, 2D materials, such as Janus monolayer (ML) WS-X (X = Se, Te) 22 and TcX 2 (X = S, Se, Te), 23 simultaneously deliver low lattice thermal conductivity and high ZT value. However, common 2D materials such as graphene (∼2000 W m −1 K −1 ), 24 MoS 2 (23.2−34.5 W m −1 K −1 ), 25 and phosphorene (24.3−83.5 W m −1 K −1 ) 26 possess high thermal conductivity, failing to meet the needs of thermoelectric applications.…”