Formation Mechanism and High Thermoelectric Performance of Cu_5+3xFe_1‐xS₄ Icosahedral Nanoparticles with Distinctive Core‐Shell Structures

Abstract

Multiply twinned particles (MTPs) demonstrate great potential in the fields of catalysis, [1,2] high-strength alloys, [3] and thermoelectric conversion, [4] due to their unique catalytic, mechanical, and thermal/ electrical transport properties, respectively, which are induced by engineered facets, internal strain, and/or high-density twin boundaries. [5][6][7][8][9][10] Specifically, in terms of thermoelectric properties, twin boundaries are expected to have a minor influence on the carrier mobility ascribed to ordered atomic arrangement; by constructing high-density twin boundaries, phonon scattering would be enhanced effectively, providing a way in reducing the lattice thermal conductivity. [4,11,12] A notable example of MTPs is an icosahedral nanoparticle, which possesses fivefold twins, exposed low-surface energy planes, and irregular strain distribution. [13][14][15][16] Such unique characteristics open up a new route to the regulation and improvement of catalytic and thermoelectric properties. [4,17] Nevertheless, the precise regulation of icosahedral morphology is rather challenging. [18] In this context, much attention has been paid to understanding the formation mechanism of icosahedral nanoparticles, [19][20][21][22] given its importance to modulating the morphological characteristics and exploiting new material systems that can form into such morphology.Great success has been achieved in the synthesis of cubicstructured metal (e.g., Pt, Ag, Au, Cu) icosahedral nanoparticles based on well-developed chemical solution methods. [16,17] Accordingly, two mechanisms for icosahedron growth were explored and put forward: one is the successive growth from a tetrahedral unit via continuous twinning, [19,23] while the other is that particle agglomerates first have fivefold twins formed in the central regions and then gradually grow and develop into an icosahedron. [19,24] The latter process is commonly accompanied by a series of dynamic processes, including diffusion, coalescence, oriented attachment, and Ostwald ripening. [25,26] Importantly, considering that the dihedral angle between two adjacent {111} twin planes is 70.53° rather than 72°, [27] strain energy would be Multiply twinned icosahedrons possess a diversity of unique functionalities well-suited to various applications, such as thermoelectric conversion. Regarding chalcogenide icosahedron, an unconventional yet promising thermoelectric candidate, disclosing its growth mechanism is rather challenging. This study uncovers the formation mechanism of thermoelectric Cu 5+3x Fe 1-x S 4 (0 ≤ x ≤ 0.4) core-shell nano-icosahedrons, which is distinct from that of wellknown metal icosahedrons. Electron microscopy and molecular dynamics simulations reveal that the evolution into icosahedrons, stemming from the fivefold twin formation in the center of Cu 5 FeS 4 particle aggregates, is accompanied by the gradual formation of Fe-rich orthorhombic-structured core and Cu-rich cubic-structured shell, which provides a peculiar stress relaxation mechanism. Further ident...

Remarkable Electrical Conductivity Increase and Pure Metallic Properties from Semiconducting Colloidal Nanocrystals by Cation Exchange for Solution‐Processable Optoelectronic Applications

“…The σ level of a-NC-C is much higher than those of previously reported bornite-type materials (10-500 S cm −1 ) or PEDOT:PSS (conducting polymer) films (1000-4000 S cm −1 ) at room temperature, and that is comparable to that of indium tin oxide (ITO, ≈10 4 S cm −1 ). [7,[78][79][80][81][82] Subsequently, we performed TEM and XRD analysis of the NC-C films before and after annealing at 250 and 500 °C to investigate the morphology and structure of highly conductive annealed NC-C films. As shown in Figure S16, Supporting Information, the size of the NCs (6.89 ± 0.60 nm) in the 250 °C-annealed-NC-C film is comparable to that in the nonannealed film (6.24 ± 0.47 nm).…”

Recent advances, challenges, and perspective of copper‐based liquid‐like thermoelectric chalcogenides: A review

“…x Fe 1Àx S 4 due to multiple twinned icosahedrons need to be explored, and this study may discover potential candidates for thermoelectricity. 130 As shown in Figure 6C,D, the inhomogeneous segregation of Cu and Fe elements results different crystal structures which can be attributed to structural transformation from cubic to orthorhombic phase. This work predicts that other icosahedral nanoparticles with different size and twin boundary can be explored to realize the TE performance in other chalcogenides.…”

“…120,121 Nevertheless, cubic structured-Cu 2 Te has exhibited some impressive TE transport properties even retaining their physicochemical properties 122,123 such as superconductor, F I G U R E 2 Graphical representation for the major synthesis, mechanisms, Cu distribution in liquid-like structure, phases transition and working module of the liquid-like Cu 2 X-based thermoelectric materials. 84,[125][126][127][128][129][130] metals/semiconductor, and ionic conductor. 69,96,124 Such characteristics suggest that chemical compositions may tune the electronic band structure of Cu 2 Te and thus lead to optimized power factor at high temperatures.…”

“…62,[161][162][163][164] and (C, D) SEM and HAADF images for corresponding EDS mappings of Cu 5+3x Fe 1Àx S 4 (x = 0.4) icosahedrons respectively. 130 Copyright 2022, Wiley-VCH GmbH.…”

Simultaneously Enhanced Thermoelectric and Mechanical Performance in SnSe-Based Nanocomposites Produced via Sintering SnSe and KCu7S4 Nanomaterials

“…Regarding the synthetic method, bottom-up solution synthesis is emerging as a highyield, low-cost method for developing novel thermoelectric nanocomposites by way of constructing heterostructures and core−shell structures. 11,41 As an extended approach to solution processing, obtaining uniform mixtures of different types of nanoparticles by blending them in solution, followed by hightemperature sintering, is regarded as a versatile strategy to produce nanocomposites with wide compositions. 28,42 If a chemical reaction between different particles is promoted and occurs, new nanoinclusions could be generated, leading to the formation of nanocomposites with extended types of secondary phases.…”