Transition Metal Chalcogenides Research Articles

Pressure-induced structural stability, metallization and optoelectronic properties of transition metal chalcogenide BaTiS3

The pressure effects on the structural stability, metallization and optoelectronic properties of transition metal chalcogenide BaTiS3 are investigated by performing ab-initio calculations. Our calculations show that BaTiS3 has a hexagonal structure at ambient pressure, which matches well with the available experimental values. As pressure increases, a transition from hexagonal to orthorhombic phase occurs at around 10.8 GPa. The band structure and density of states of hexagonal BaTiS3 have been calculated and analysed. Moreover, the effect of pressure on the optical properties has been studied in terms of dielectric function as well as absorption coefficient, reflectivity and extinction coefficient. The application of hydrostatic pressure has shifted the maximum absorption toward the visible range, revealing that hexagonal BaTiS3 can be used for high pressure optoelectronic applications.

Crystallographic Dimensionality Determines the Electrochemical Reaction Mechanism in Alkali Transition-Metal Chlorides.

Intense research efforts on transition metal chalcogenides (oxides and sulfides), pnictides (nitrides and phosphides), and fluorides have demonstrated the complex, intertwined effects of structural and chemical changes on their electrochemical response leading to intercalation, conversion, or displacement reactions when reacting with lithium. Prior efforts largely left halides unexplored due to their heightened solubility in classical liquid electrolytes. In this work, we employ superconcentrated electrolytes to demonstrate the composition- and structure-dependent electrochemical reactivity of A2MCl4 compounds (A = Li or Na and M = Cr, Mn, Fe, and Co). Comparing four lithiated compounds, we demonstrate that they all undergo conversion reactions when reacting with 2 Li+ per formula unit, associated with large polarization and limited cycling ability. Nevertheless, combining in situ XRD with post-mortem XPS and STEM/EDS analysis, we demonstrate that Li2CoCl4 first reacts with one Li+ following a displacement reaction providing a reversible capacity of 125 mAh g-1. This reaction is enabled by the formation of a Li6CoCl8 intermediate, which shares a similar anionic framework with pristine Li2CoCl4, ensuring the topotactic insertion of Li+ balanced by the Co2+/Co0 redox couple and the formation of metallic Co nanoparticles. Comparing these compounds, we propose that two criteria are necessary to trigger the displacement reaction in A2MCl4 compounds: the presence of 1D chains of edge-sharing octahedra to favor electronic delocalization and the availability of a metal-deficient intermediate. Screening numerous A2MCl4 compounds, we demonstrate the universality of these design principles, which extend to Na-ion materials by demonstrating a low-polarization, reversible displacement reaction for Na2MnCl4.

Pressure induced semiconductor-like to metal transition and linear magnetoresistance in Cr2S2.88 single crystal.

The transition metal chalcogenide Cr2S3-x has unique properties, such as a lower antiferromagnetic transition temperature, semiconducting behavior, and thermoelectric properties. We focus on the effects of high pressure on the properties of electrical transport and structure in the single crystal Cr2S2.88. It is observed that the resistance drops abruptly by approximately two orders of magnitude and the temperature derivative of the resistance changes from negative to positive after 15.7 GPa. The Cr2S2.88 crystal has undergone transitions from a semiconductor-like phase to a metal I phase and then to another metal II phase. Simultaneously, a structural phase transition after 16.1 GPa is confirmed by synchrotron angle dispersive X-ray diffraction (AD-XRD). After the structural phase transition, the negative magnetoresistance becomes positive with increasing pressure and shows a linear relationship in the metal II phase. Electron-type carriers dominate in the semiconductor-like phase, but hole-type carriers dominate after the structural phase transition. Our work provides an example of the effective modulation of semiconductor-like properties by pressure, which is meaningful for the innovation and development of semiconductor technology.

Enhanced Sodium Storage in MXene Transition Metal Chalcogenides Anode through Dual Molten Salt Etching

Referred to as potential options for anodes in sodium-ion batteries, transition metal chalcogenides (TMCs) exhibit unique electronic and structural characteristics. However, the limited electrical conductivity inherent in them poses a hindrance to electron transport, while their tendency to undergo volumetric expansion during cycling exacerbates structural instability, thereby imposing constraints on practical applications. Herein, a dual molten salt etching strategy followed by a sulfidation-selenidation process was employed to anchor multi-component sulfides FeS2/NiS and FeSe/NiSe onto conductive Ti3C2Tx MXene, achieving superior sodium storage performance. Owing to the enhanced Na⁺ and faster kinetics of electronic transport, mechanical strain is effectively reduced, and strong covalent interactions are formed at the interface, significant enhancement in the cycling stability is observed for the anodes of Ti3C2Tx@FeS2/NiS and Ti3C2Tx@FeSe/NiSe (with specific capacities of 309.4 and 162.6 mAh g−1, respectively, after 1000 cycles at 5 A g−1, with a former retention capacity rate that can reach as high as 87.8%) and exceptional rate performance (252.1 and 207.8 mAh g−1, respectively, at 8 A g−1). Furthermore, full cells assembled by pairing Ti3C2Tx@FeS2/NiS and Ti3C2Tx@FeSe/NiSe with Na3V2(PO4)3 cathodes also demonstrate excellent cycling performance, with both configurations achieving up to 500 cycles. The suggested approach enables efficient utilization of byproducts from Lewis acidic etching, expanding possibilities for synthesizing high-performance anodes in sodium-ion batteries consisting of MXene and TMCs.

Hierarchical core-shell transitional metal chalcogenides Co9S8/ CoSe2@C nanocube embedded into porous carbon for tunable and efficient microwave absorption

In the domain of electromagnetic (EM) wave absorbing materials, the selection of suitable components and microstructures is an effective approach for designing the intense coupling of wave impedance and EM dissipation. In this study, we have successfully fabricated a double-carbon modified Co9S8/CoSe2 nanocube, where the core-shell Co9S8/CoSe2@C cube was anchored onto porous carbon (PC). The existence of three-dimensional (3D) porous carbon and the fabrication of Co9S8/CoSe2@C distributed on carbon nanosheets contribute to the improvement of conduction, magnetic losses, and the optimization of impedance matching. Substantial heterogeneous interfaces are generated between Co9S8, CoSe2, carbon shells, and PC, leading to extensive interfacial polarization and facilitating the transformation of EM energy into thermal energy. The abundant defects, S and Se vacancies in carbon component can act as polarization centers, inducing dipolar polarization and thus increasing the electromagnetic wave (EMW) loss. The Co9S8/CoSe2@C@PC exhibits the best microwave absorption properties, with a minimum reflection loss (RLmin) of −64.1 dB at 2.5 mm and an effective absorption bandwidth (EAB) of 6.3 GHz. The High-Frequency Structure Simulator results indicate the RCS values of the samples within the range of -90 °C < θ < 90 °C are lower than -20 dB m2, which can achieve almost full-angle coverage in the actual environment. This research offers inspiration and strategies for the design and synthesis of multi-component magneto-electric composites based on transitional metal chalcogenides.

Hollow transition metal chalcogenides derived from vanadium-based metal organic framework for hybrid supercapacitors with excellent energy-density and stability

Hollow transition metal chalcogenides derived from vanadium-based metal organic framework for hybrid supercapacitors with excellent energy-density and stability

Mott resistive switching initiated by topological defects

Avalanche resistive switching is the fundamental process that triggers the sudden change of the electrical properties in solid-state devices under the action of intense electric fields. Despite its relevance for information processing, ultrafast electronics, neuromorphic devices, resistive memories and brain-inspired computation, the nature of the local stochastic fluctuations that drive the formation of metallic regions within the insulating state has remained hidden. Here, using operando X-ray nano-imaging, we have captured the origin of resistive switching in a V2O3-based device under working conditions. V2O3 is a paradigmatic Mott material, which undergoes a first-order metal-to-insulator phase transition together with a lattice transformation that breaks the threefold rotational symmetry of the rhombohedral metallic phase. We reveal a new class of volatile electronic switching triggered by nanoscale topological defects appearing in the shear-strain based order parameter that describes the insulating phase. Our results pave the way to the use of strain engineering approaches to manipulate such topological defects and achieve the full dynamical control of the electronic Mott switching. Topology-driven, reversible electronic transitions are relevant across a broad range of quantum materials, comprising transition metal oxides, chalcogenides and kagome metals.

Strain- and Carrier-Engineered Electromagnetic Properties in Transition-Metal Chalcogenide Monolayers: Implications for Nanoscale Spintronic Devices

Strain- and Carrier-Engineered Electromagnetic Properties in Transition-Metal Chalcogenide Monolayers: Implications for Nanoscale Spintronic Devices

2D Transition Metal Chalcogenides (TMDs) for Electrocatalytic Hydrogen Evolution Reaction: A Review.

Since the MoS2 synthesis, the family of two-dimensional transition metal chalcogenides (TMDs) have been intensively explored theoretically and experimentally. TMDs endowed with adjustable electronic, physical and chemical properties lead to increasing interest in the application of energy storage, molecule detection and catalysis. In the mini review, we present a forward-looking summary of 2D TMDs in hydrogen evolution electrocatalysis, including synthesis methods, hydrogen evolution performance, and optimization strategies. This review will deepen the fundamental understanding of the physical-chemical properties of TMDs with different phases and contribute unveil the universal principle among electronic configuration, atomic arrangement, physical and chemical property for the material design.

Pressure-induced band gap enhancement and temperature-dependent thermoelectric characterization of semiconducting Transition Metal Chalcogenides LiMS (M = Cu, Ag)

The first principles study of Transition Metal Chalcogenides LiMS (M = Cu, Ag) has been conducted utilizing the concepts of Density Functional Theory (DFT). Both the compounds possess a cubic structure with space group F-43m. The mechanical stability of LiCuS and LiAgS has been predicted based on the values of elastic tensor. These Chalcogenides possess an interesting electronic band structure which reveals their semiconducting nature with a direct band gap. The electronic structure is further subjected to high pressure and the changes in band gap are deeply observed. For these materials, the changes in band gap in response to applied pressure suggest the possibility of their use in band gap engineering. The phonon curves are investigated over the Brillouin zone's high symmetry directions which reveal the lattice dynamical stability of the presently studied compounds. Moreover, the atoms present at different positions inside a crystal lattice exhibit vibrations of different intensities and in different directions which have been studied through the Eigenvector representations. The thermoelectric properties of LiCuS and LiAgS have been characterized using Boltzmann's theory over the range of temperature between 100 K and 1600 K. The calculated thermoelectric parameters reveal the high thermoelectric efficiency of these materials with excellent values of the figure of merit. The interesting properties of ternary Chalcogenides LiMS (M = Cu, Ag) make them promising candidates for thermoelectric applications.

Atomic layer deposition of transition metal chalcogenide TaSx using Ta[N(CH3)2]3[NC(CH3)3] precursor and H2S plasma

As a transition metal chalcogenide, tantalum sulfide (TaSx) is of interest for semiconductor device applications, for example, as a diffusion barrier in Cu interconnects. For deposition of ultrathin nanolayers in such demanding 3D structures, a synthesis method with optimal control is required, and therefore, an atomic layer deposition (ALD) process for TaSx was developed. ALD using (tert)-butylimidotris(dimethylamido)tantalum (Ta[N(CH3)2]3[NC(CH3)3]) as the precursor and an H2S-based plasma as the coreactant results in linear growth of TaSx films as a function of the number of cycles for all temperatures in the range 150–400 °C with growth per cycle values between 1.17±0.03 Å and 0.87±0.08 Å. Saturation of the precursor and plasma dose times, established at 300 °C, was reached after 20 and 10 s, respectively. Variation of the table temperature or the plasma composition offers the possibility to tune the film properties. At 300 °C, amorphous TaS3 films were grown, while addition of H2 to the plasma led to polycrystalline TaS2 films. The difference in sulfur content in the films correlates to a change in resistivity, where the least resistive film had the lowest S content.

Observation of kagome-like bands in two-dimensional semiconducting Cr8Se12

The kagome lattice is a versatile platform for investigating correlated electronic states. However, its realization in two-dimensional (2D) semiconductors for tunable device applications is still challenging. An alternative strategy to create kagome-like bands is to realize a coloring-triangle (CT) lattice in semiconductors through a distortion of a modified triangular lattice. Here, we report the observation of low-energy kagome-like bands in a semiconducting 2D transition metal chalcogenide—Cr8Se12 with a thickness of 7 atomic layers—which exhibits a CT lattice and a bandgap of 0.8 eV. The Cr-deficient layer beneath the topmost Se-full layer is partially occupied with 2/3 occupancy, yielding a √3 × √3 Cr honeycomb network. Angle-resolved photoemission spectroscopy measurements and first-principles investigations reveal the surface kagome-like bands near the valence band maximum, which are attributed to topmost Se pz orbitals modulated by the honeycomb Cr.

Topological Polar Networks in Twisted Rhombohedral-Stacked Bilayer WSe2 Moiré Superlattices.

Sliding ferroelectricity enables materials with intrinsic centrosymmetric symmetry to generate spontaneous polarization via stacking engineering, extending the family of ferroelectric materials and enriching the field of low-dimensional ferroelectric physics. Vertical ferroelectric domains, where the polarization is perpendicular to atomic motion, have been discovered in twisted bilayers of inversion symmetry broken systems such as hexagonal boron nitride, graphene, and transition metal chalcogenides. In this study, we demonstrate that this symmetry breaking also induces lateral polar networks in twisted bilayer rhombohedral-stacked WSe2, as determined through symmetry considerations and vector piezoresponse force microscopy (V-PFM) results. Lateral polarization (LP) in saddle point (SP) regions forms head-to-tail triangular vortices, exhibiting elliptical domain shapes with widths up to 40 nm. The LP encloses the vertical polarization (VP), forming a network of Bloch-type merons and antimerons. Our work enhances the understanding of domain distribution and polarization orientation in moiré ferroelectrics.

Machine learning assisted screening of two dimensional chalcogenide ferromagnetic materials with Dzyaloshinskii Moriya interaction

Magnetic skyrmions are potential candidates for high-density storage and logic devices because of their inherent topological stability and nanoscale size. Two-dimensional (2D) Janus transition metal chalcogenides (TMDs) are widely used to induce skyrmions due to the breaking of inversion symmetry. However, the experimental synthesis of Janus TMDs is rare, which indicates that the Janus configuration might not be the most stable MXY structure. Here, through machine-learning-assisted high-throughput first-principles calculations, we demonstrate that not all MXY compounds can be stabilized in Janus layered structure and a large proportion prefer to form other configurations with lower energy than the Janus configuration. Interestingly, these new configurations exhibit a strong Dzyaloshinskii–Moriya interaction (DMI), which can generate and stabilize skyrmions even under a strong magnetic field. This work provides not only an efficient method for obtaining ferromagnetic materials with strong DMI but also a theoretical guidance for the synthesis of TMDs via experiments.

Insights into the Effect of Crystal Facets and Sulfur Defects on the Product Selectivity of Various CdS Configurations for CO2 Photoreduction: A DFT Study

CO2 photoreduction into valuable hydrocarbons, such as CO, CH4, and C2H4, delivers a promising approach to address both environmental and energy challenges. Transition metal chalcogenides, particularly cadmium sulfide (CdS), have emerged as prominent candidates due to their tunable electronic properties and availability. This study delves into a comprehensive investigation of how CdS crystalline facets and sulfur-deficient surfaces modulate the product selectivity. Through employing density functional theory (DFT), we unravel the catalytic performance of various CdS crystal orientations and sulfur vacancy configurations. The results have shown that different CdS facets exhibit unique electronic characteristics and surface energetics, which influence the adsorption dynamics and reaction pathways. The introduction of sulfur vacancies further modulates the nature of active sites, leading to substantial shifts in product selectivity. A detailed investigation on the reaction mechanisms unveils that specific facets preferentially facilitate the formation of CO, while others are more conducive to the generation of hydrocarbons such as CH4 and C2H4, due to the variations in activation barriers and intermediate stabilities. These findings underscore the importance of crystal facet engineering and defect manipulation in tailoring catalyst performance thus providing valuable insights for the rational design of efficient and selective CO2 reduction metal catalysts.

Chalcogen and halogen surface termination coverage in MXenes—structure, stability, and properties

MXenes are a diverse family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides. They can be synthesized through both top-down approaches, such as selective etching of A-layers from MAX phases using acids or molten salts, and bottom-up approaches, such as direct synthesis using chemical vapor deposition. However, the degree of the surface termination coverage depends on the synthesis route and is one key parameter for controlling its properties. This study focuses on halogen- and chalcogen-terminated MXenes, particularly M2CTx where M = Ti, Zr, V, Nb, Ta, and T = S, Se, Te, Cl, Br, I, and with surface termination coverage ranging from 100% (ideal, x = 2) to 50% (x = 1). The incorporation of oxygen on vacant termination sites was also evaluated. Using density functional theory (DFT) calculations, we investigated the structural, electronic, and mechanical properties of these MXenes. Our findings reveal that non-ideal termination coverage (x < 2) is more favorable for MXenes terminated with a larger size of T, such as Ti2CBrx, Nb2CClx, and Ta2CClx, and leads to mixed termination sites and lower binding energies. A reduced binding energy may facilitate delamination into single sheets, however, too low termination coverage may also cause structural collapse. Electronic properties showed an increased number of states at the Fermi level under non-ideal coverage, potentially enhancing the conductivity. Mechanically, we find the moduli of MXenes to be comparable to other 2D materials, such as transition metal chalcogenides and hexagonal boron nitride, indicating their suitability for applications requiring flexibility and durability. This study underscores the potential of tailoring MXene properties through precise control of termination coverage and composition, paving the way for enhanced application-specific performance.

Enhanced Hydrogen Evolution Reaction Activity through Bimetallic Phosphide Integration in ReS2/Re2O7 Heterostructure

AbstractDeveloping a nonprecious and sustainable electrocatalyst in clean energy generation is quite noteworthy. Transition metal chalcogenides, oxides, and phosphides have emerged as promising candidates to substitute Pt‐based catalysts. In this study, we explore the catalytic potential of ReS2, a promising member of the transition metal dichalcogenides (TMD) family, for hydrogen evolution reactions (HER). The formation of rhenium oxide during the synthesis of ReS2 and further incorporation of a bimetallic phosphide NiCuP in a sequential hydrothermal synthesis reveals an excellent HER activity, as demonstrated by photoelectrochemical and electrochemical studies. Notably, the catalyst exhibits a significantly lower overpotential of −0.10 V (corresponding to −10 mA/cm2) and achieves a high current density of approx. −271 mA/cm2 at −0.79 V versus reversible hydrogen electrode (RHE) under light irradiation. The catalyst demonstrates high stability. These findings underscore the potential of NiCuP‐integrated ReS2/Re2O7 as a highly efficient and sustainable catalyst for HER.

Structural and dynamical properties of two dimensional disordered metal chalcogenides AB (A [formula omitted] Zn, Cd; B [formula omitted] S, Se): A classical molecular dynamic study

In recent years, the synthesis of two-dimensional (2D) materials, particularly the crystalline and disordered phases of 2D transition metal chalcogenides (TMCs), has gained considerable attention due to their wider electronic band gaps. This distinctive feature is pivotal in shaping their potential applications in solar cells, sensors, field-effect transistors (FETs), and photocatalysis for water decomposition. In the present study, we report molecular dynamics simulation of 2d disordered configuration of ZnX and CdX (X: S, Se) compounds using the Stillinger–Weber potential. We have explored their structural features by calculating their radial distribution functions and ring statistics. These systems are thermodynamically stable. The disordered network with numerous voids in these compounds play a pivotal role in lowering their melting temperature compared to their 2D crystalline counterparts, which falls within the range of 600 K to 700 K. The phonon density of states for all these systems shows a higher number of lower frequency (acoustic) modes than optical modes, which is understandably due to the presence of open regions and 2-fold sites in such systems.

Photocarrier relay modulating solar CO2-to-Syngas conversion

Solar-driven syngas generation by CO2 reduction provides a sustainable strategy to produce renewable fossil fuels. Nevertheless, this promising approach often suffers from tough CO2 activation, sluggish reaction kinetics and complex selectivity. Herein, we exquisitely constructed spatially directional charge transport channel over two-dimensional transition metal chalcogenide (TMC)-based heterostructure via a facile and universal electrostatic self-assembly method. Tailor-made positively charged non-conjugated insulating polymer of poly(diallyl-dimethyl-ammonium chloride) (PDDA) and negatively charged graphene oxide (GO) precursor as building blocks are controllably anchored on the TMC substrate, by which ultrathin PDDA layer is intercalated at the interface of GO and TMC. We ascertain that, in this customized sandwiched heterostructures, PDDA interim layer functions as an electron-relaying mediator, whilst graphene (GR) obtained from in-situ GO reduction during the photocatalytic reaction serves as a terminal electron-trapping reservoir, synergistically facilitating the spatially vectorial charge separation/migration over TMC, thus endowing the TMC/PDDA/GR heterostructures with conspicuously enhanced visible-light-driven photoactivity toward CO2-to-syngas conversion. Our work would inspire judicious ideas for finely modulating charge transfer over polymer-mediated photosystems and benefit our fundamental understanding of solar CO2 conversion.

Controlled Synthesis and Phase Transition Mechanisms of Palladium Selenide: A First-Principles Study.

Using density functional theory, we carefully calculated the relative stability of monolayer, few-layer, and cluster structures with Penta PdSe2, T-phase PdSe2, and Pd2Se3-phase. We found that the stability of Penta PdSe2 increases with the number of layers. The Penta PdSe2, T-phase PdSe2, and Pd2Se3 monolayers are all semiconducting, with band gaps of 1.77, 0.81, and 0.65 eV, respectively. The formation energy of palladium selenide clusters with different phase structures is calculated, considering the cluster size, stoichiometry, and chemical environment. Under typical experimental conditions, Pd2Se3 phase clusters are found to be dominant, having the lowest formation energy among all of the phases considered, with this dominance increasing as cluster size grows. Adjusting the Pd-Se ratio in the environment allows for controlled synthesis of specific palladium selenide phases, providing theoretical insights into the nucleation mechanisms of PdSe2 and other transition metal chalcogenides.