Texturization-Induced In-Plane High-Performance Thermoelectrics and Inapplicability of the Debye Model to Out-of-Plane Lattice Thermal Conductivity in Misfit-Layered Chalcogenides

Abstract

Texturization tuning is of crucial significance for designing and developing high-performance thermoelectric materials and devices. Here, we report for the first time that a strong texturization effect induces an in-plane high-performance thermoelectric and an out-of-plane low lattice thermal conductivity in Sb-substituted misfit-layered (SnS)1.2(TiS2)2 alloys. In the in-plane direction, the oriented texture promotes a high carrier mobility, contributing to the maximization of the power factor (∼0.90 mW K–2 m–1). Moreover, the in-plane lattice thermal conductivity dramatically reduces deriving from the point defects due to the Sb substitution and weakened transverse sound velocity owing to the softening of bonding, ultimately leading to one of the highest thermoelectric performances ever reported among misfit-layered chalcogenides. In particular, in the out-of-plane direction, the texturization triggers the lowest lattice thermal conductivity (∼0.39 W K–1 m–1), exceeding the theoretical limit of the Debye–Cahill model, which provides a precious opportunity to investigate this real Sb-substituted (SnS)1.2(TiS2)2 material. The present finding in misfit-layered chalcogenides provides a novel strategy for manipulating thermoelectrics via texturization engineering.

Nanoengineering of Tin Monosulfide (SnS)‐Based Structures for Emerging Applications

“…Additionally, in 2019, polycrystalline misfit-layered antimony (Sb)-substituted SnS/TiS 2 alloys were successfully synthesized by a solid-state reaction method and systematically investigated for their anisotropically thermoelectric properties in a wide temperature range (320-720 K). [239] The HAADF-STEM image and SAED pattern confirm the layered structure of the misfit-layered superlattice, where a single SnS layer and double TiS 2 layers are stacked alternatively along the c-axis (Figure 24d). The TiS 2 layers separated by van der Waals act as conductive species while the SnS layer can be regarded as a barrier layer to suppress phonon transmission.…”

“…Thermoelectric (TE) materials can make it come true for the effective conversion between electric and thermal energies by virtue of thermoelectric effect. [9][10][11]14,104,164,239,240] Harvesting electricity by utilizing waste heat is a clean and sustainable approach to overcome the challenge of the traditional fuel resource consumption, making thermoelectrics become a research hotspot with remarkable attentions for extensive application prospects. [241][242][243][244][245][246][247] The conversion efficiency of a TE material is usually dependent on the dimensionless figure of merit (ZT), defined as ZT ¼ (S 2 σ/κ)T, where S is Seebeck coefficient, σ is electrical conductivity, and κ is total thermal conductivity including the lattice part (κ L ) and the electronic part (κ e ).…”

“…SnS with an electronic band structure exhibits low thermal conductivity, favorable transport properties, and the controlled carrier concentration by simply extrinsic doping, making it a promising candidate in the community of thermoelectric power generation. [240,242,248] To further improve the TE performance, nanoengineering approaches, such as doping SnS with heteroatoms or alloying SnS with metals or metal chalcogenides, [104,164,239,240,242,249,250] provide an alternative way to optimize the ZT of SnS-based nanostructures for next-generation thermoelectrics. For example, in 2018, Yin et al [250] reported successful synthesis of SnS nanocrystals and applied the flexible SnS thin films for high-performance flexible thermoelectrics.…”

Strong Anisotropic Thermal Conductivity in Polycrystalline Layers of (AgxSn1‐xS)1.2(TiS2)2 with Prospects Toward Improved Thermoelectric Performance

“…Recently, effective strategies such as carrier concentration optimization, [22] density-of-state resonance, [23] promotion of carrier mobility, [24] all-scale hierarchical architectures, [25] low phonon velocity, [26] and low specific heat, [27] are widely used to improve the zT values, which are also applicable to the misfit-layered sulfides. For instance, improving carrier mobility, [28,29] optimizing carrier concentration, [30,31] and enhancing density-of-state distortion [32,33] are utilized to promote the electrical transport properties of (MS) 1+m (TiS 2 ) 2 . Alternatively, softening lattice [29,34] or introducing planar defects of translational displacement and stacking faults [35][36][37] are also adopted to minimize thermal conductivity.…”

“…For instance, improving carrier mobility, [28,29] optimizing carrier concentration, [30,31] and enhancing density-of-state distortion [32,33] are utilized to promote the electrical transport properties of (MS) 1+m (TiS 2 ) 2 . Alternatively, softening lattice [29,34] or introducing planar defects of translational displacement and stacking faults [35][36][37] are also adopted to minimize thermal conductivity. However, the above obtained highest possible zT mainly occurred in the in-plane direction while the out-of-plane properties have garnered less attention.…”