Se Substitution Research Articles

Extending Se substitution to the limit: from 5S to 5Se in high-efficiency non-fullerene acceptors.

Based on the newly synthesized seleno[3,2-b]selenophene unit, two near-infrared non-fullerene acceptors (NFAs) of 4Se and 5Se are constructed by replacing four or all sulfurs with selenium in high-efficiency Y-series NFAs. Consequently, binary devices based on 4Se and 5Se afford PCEs of 15.17% and 15.23%, respectively, with a photoelectric response approaching 1000 nm. More excitingly, the energy loss of the 5Se-based device was as low as 0.477 eV along with almost the smallest non-radiative loss of ∼0.15 eV thus far.

MAX phases Hf2(SexS1−x)C (x = 0–1) and their thermal expansion behaviors

Herein, a series of chalcogen-containing MAX phases, Hf2(SexS1−x)C, were successfully synthesized, whose lattice parameter change follows the Vegard’s law. The average coefficient of thermal expansion (CTE) can be continuously tuned from 7.59 μK−1 to 9.93 μK−1 when the occupancy rate x of Se changes from 0 to 1. The substitution of Se for S effectively soften the crystal structures that is reflected by long average M-A bond in Se-alloying Hf2(SexS1−x)C. However, the CTEs along a and c axes in all Hf2(SexS1−x)C MAX phases are almost same which may be find application in thermal barrier coating (TBC) that isotropic volume change is highly demanding.

Anion-tuning of cobalt-based chalcogenides for efficient oxygen evolution in weakly alkaline seawater

Regulating the electronic structure is of great importance for improving the performance, stability, and selectivity of seawater splitting catalysts. Herein, cobalt-based oxide and chalcogenide (Co3X4, X = O, S, and Se) are synthesized to investigate the effect of anions on the electronic structure, catalytic performance and selectivity of the seawater oxidation catalysts. The theoretical calculations predict the possible active sites of oxygen evolution reaction and hypochlorite evolution reaction. Then the experimental characterization and calculation results demonstrate that S and Se substitution could regulate the electronic structure and d-band center of Co site, enhance the metallicity of catalysts. Moreover, the energy barrier of Cl* conversion to ClO- could be modulated for preventing the formation of ClO- by anions regulating. Consequently, Co3S4 could stably operate at a current density of 100 mA cm−2 in 0.1 M KOH + 0.6 M NaCl for 100 h and in neutral seawater for 20 h.

Room temperature magnetocaloric effect in CrTe1−xSex alloys

In this work, we report room temperature magnetocaloric properties in CrTe1−xSex (0.00 ≤ x ≤ 0.10) alloys prepared by a conventional solid-state reaction. The Rietveld refinement of the XRD pattern of CrTe1−xSex showed the emerging of pure hexagonal NiAs structure with P63/mmc (194) space group with increasing Se substitution. Upon μ0H = 5 T applied magnetic field, the magnetocaloric effect analysis revealed maximum magnetic entropy change $$(\Delta {S}_{M})$$ in the range 7.9–9.2 J/kg K−1 with a relative cooling power (RCP) value of about 550–694 J/kg. The RCP values exceed the corresponding RCP value of the prototype Gd element near room temperature. The obtained results suggest that CrTe1−xSex (0.00 ≤ x ≤ 0.10) alloys is a viable candidate for a room temperature magnetic cooling application.

Crystal structure and properties of layered compounds Fe0.75TiS2–ySey

Layered compounds Fe0.75TiS2–ySey (0 ≤ y ≤ 1) with a metal-to-chalcogen ratio of 7:8 and a monoclinic crystal structure were obtained for the first time by a three-stage solid-phase method and studied by x-ray diffraction and by measuring electrical resistivity, magnetic susceptibility, and magnetization. The substitution of Se for S in the compounds results in an enhancement of the anisotropy of the crystal lattice deformations apparently due to an increase in the covalency of chemical bonds. An increase in the Se content in Fe0.75TiS2–ySey to y = 1.0 leads to a decrease in the magnetic critical temperature Tcrit from 145 K to ∼100 K and to a change in the magnetic behavior from ferrimagnetic toward antiferromagnetic. The higher values of electrical resistivity of Fe0.75TiS2–ySey in magnetically ordered state compared to those observed in the disordered paramagnetic state have been attributed to the inhomogeneity of the magnetic state in this compound below Tcrit due to the mixing of Fe and T atoms in cationic layers.

First-principles study on selenium-doped Li10GeP2S12 solid electrolyte: Effects of doping on moisture stability and Li-ion transport properties

Improving moisture stability without degrading the ionic conductivity of Li10GeP2S12 (LGPS) based solid-state electrolytes (SSEs) is one of the key issues in developing all-solid-state lithium batteries. Herein, we report the reactivity of the LGPS surface towards H2O, subsequent hydrolysis reactions for the H2S formation, and effective methods to suppress the H2S evolution on the LGPS surface using density functional theory (DFT) calculations. The pristine LGPS surface is highly unstable towards H2O at room temperature, where H2O dissociation occurs spontaneously. However, the H2O adsorption and its activation are weakened upon the Se substitution on the LGPS surface. By doping the Se atom on LGPS, the H2S evolution can be suppressed and significantly improve the chemical stability of the LGPS surface. In addition, we predict the Li+ ion transport properties of both pristine and Se-doped LGPS compounds using ab initio molecular dynamics (AIMD) simulations. The Se-doped LGPS material has a similar bandgap to pristine LGPS; it can have similar decomposition products and low electronic conductivity. The predicted ionic conductivity of Se-doped LGPS is found to be slightly lower than the pristine. We propose replacing sulfur with Se atom as an effective strategy to improve the moisture stability of the LGPS compound.

Phase transformation and grain growth in spray deposited wurtzite CuInS2 films

We report the processing of large-grained chalcopyrite-CuIn(S,Se)2 (ch-CISSe) films using spray deposition of wurtzite-CuInS2 (wz-CIS) nanoparticle ink and subsequent selenization. Wurtzite to chalcopyrite phase transformation and grain growth were studied at varying selenization temperatures of 350, 400, 450, 500 and 550 °C for 15 min. On annealing in selenium (Se) atmosphere at 400 °C, the film transformed from wurtzite to chalcopyrite phase completely, while the grain growth took place at higher temperatures (500–550 °C), requiring greater amounts of Se substitution (Se/Se + S > 0.7). Differential scanning calorimetry (DSC) indicates that the phase transformation temperature is sensitive to the heating rate and has a second-order character.

Two-step Mott transition in Ni(S,Se)2 : μSR studies and charge-spin percolation model

A pyrite system ${\mathrm{NiS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ exhibits a bandwidth controlled Mott transition via (S,Se) substitutions in a two-step process: the antiferromagnetic insulator (AFI) to antiferromagnetic metal (AFM) transition at $x\ensuremath{\sim}0.45$ followed by the AFM to paramagnetic metal (PMM) transition at $x\ensuremath{\sim}1.0$. Among a few other Mott systems which exhibit similar two-step transitions, $\mathrm{Ni}{(\mathrm{S},\mathrm{Se})}_{2}$ is of particular interest because a large intermediate AFM region in the phase diagram would provide unique opportunities to study the interplay between the spin and charge order. Muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements on ${\mathrm{NiS}}_{2\ensuremath{-}x}{\mathrm{Se}}_{x}$ have been carried out on seven different Se concentrations from $x=0$ to 1.0. The results on quantum evolution demonstrate significantly random spin correlations in the AFM region associated with a rapid reduction of the average local static Ni moment size with increasing $x$, yet without signatures of macroscopic phase separation as confirmed by nearly full volume fraction participating in the static muon relaxation process up to $x\ensuremath{\sim}$ 0.9 at low temperatures. The observed time spectra in the AFM region indicate Lorentzian distribution of static internal field expected for a spatially dilute spin structure. No signature of dynamic critical behavior was observed in thermal phase transitions. The previous neutron scattering studies found sharp magnetic Bragg peaks with a slower reduction of the average ordered moment size in the AFM region. By comparing and combining the muon and neutron results, here we propose a picture where the spin order is maintained by the percolation of ``nonmetallic'' localized and dangling Ni moments surrounded by S, while the charge transition from AFI to AFM is caused by the percolation of the conducting paths generated by the Ni-Se-Ni bonds. This model of interpenetrating charge and spin percolation captures the behavior of experimental results on (a) Se concentration for the insulator to metal transition, (b) Se concentration for the AFM to PMM transition, (c) variation of Hall effect in the AFM region due to conducting Ni charges on the backbone of the percolating charge network, (d) evolution of the neutron Bragg intensity, (e) evolution of the muon static local fields, and (f) spatial variation of the local conductance observed by STM.

S-doping induced phase engineering of MoSe2 for hydrogen evolution reaction

MoSe2 is a promising electrocatalyst for hydrogen evolution reaction (HER). It is confirmed that 1T-MoSe2 shows better activity for HER compared with 2H-MoSe2 since of wider interlayer spacing, higher conductivity and better hydrophilicity of 1T-MoSe2. Realization of 1T-MoSe2 is still a thorny issue due to its high formation barrier and thermodynamic metastable. Herein, considering the microstrain induced by atomic size mismatch through the substitution of Se by S, the MoSe2-2xS2x is prepared via one-pot hydrothermal synthesis, resulting in 70.3% high-purity 1T phase. Additionally, the MoSe2-2xS2x shows a low overpotential of 167 mV at 10 mA cm−2, Tafel slope of 54 mV dec−1, high double layer capacitance (Cdl) of 13.43 mF cm−2 and superior cycle stability. The results are ascribed to larger interlayer spacing, high conductivity and good hydrophilicity of 1T phase MoSe2-2xS2x. This study provides a simple and feasible route to achieve high-purity TMDs for promoting HER application.

Modulating eg orbitals through ligand engineering to boost the electrocatalytic activity of NiSe for advanced lithium-sulfur batteries

Accelerating the sluggish redox kinetics of lithium polysulfides (LiPSs) by electrocatalysis is essential to achieve high performance lithium-sulfur (Li-S) batteries. However, the issue of insufficient catalytic activity remains to be addressed. Herein, a strategy of modulating eg orbitals through ligand engineering has been proposed to boost the catalytic activity of NiSe for rapid LiPSs redox conversion. The X-ray spectroscopic measurements and theoretical calculations reveal that partial substitution of Se with N disrupts the octahedral coordination of Ni atoms in NiSe, leading to the reduced degeneracy and upward shift of eg orbitals of Ni 3d states. As a consequence, the bonding strength of N-substituted NiSe (N-NiSe) with LiPSs is enhanced, which facilitates the interfacial charge transfer kinetics and accelerates the LiPSs redox kinetics. Therefore, the Li-S batteries assembled with N-NiSe present a high capacity of 682.6 mAh g−1 at a high rate of 5 C and a high areal capacity of 6.5 mAh cm−2 at a high sulfur loading of 6 mg cm−2. This work provides a promising strategy to develop efficient transition-metal based electrocatalysts for Li-S batteries through eg orbital modulation.

Controlling Spin-Orbit Coupling to Tailor Type-II Dirac Bands.

NiTe2, a type-II Dirac semimetal with a strongly tilted Dirac band, has been explored extensively to understand its intriguing topological properties. Here, using density functional theory calculations, we report that the strength of the spin-orbit coupling (SOC) in NiTe2 can be tuned by Se substitution. This results in negative shifts of the bulk Dirac point (BDP) while preserving the type-II Dirac band. Indeed, combined studies using scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy confirm that the BDP in the NiTe2-xSex alloy moves from +0.1 eV (NiTe2) to -0.3 eV (NiTeSe) depending on the Se concentrations, indicating the effective tunability of type-II Dirac Fermions. Our results demonstrate an approach to tailor the type-II Dirac band in NiTe2 by controlling the SOC strength via chalcogen substitution. This approach can be applicable to different types of topological materials.

Controlling magnetic exchange and anisotropy by nonmagnetic ligand substitution in layered MPX3 ( M=Ni , Mn; X=S , Se)

Recent discoveries in two-dimensional (2D) magnetism have intensified the investigation of van der Waals (vdW) magnetic materials and further improved our ability to tune their magnetic properties. Tunable magnetism has been widely studied in antiferromagnetic metal thiophosphates MPX3. Substitution of metal ions M has been adopted as an important technique to engineer the magnetism in MPX3. In this work, we have studied the previously unexplored chalcogen X substitutions in MPX3 (M = Mn/Ni; X = S/Se). We synthesized the single crystals of MnPS3-xSex (0 < x < 3) and NiPS3-xSex (0 < x < 1.3) and investigated the systematic evolution of the magnetism with varying x. Our study reveals the effective tuning of magnetic interactions and anisotropies in both MnPS3 and NiPS3 upon Se substitution. Such efficient engineering of the magnetism provides a suitable platform to understand the low-dimensional magnetism and develop future magnetic devices.

Enabling Reversible Reaction by Uniform Distribution of Heterogeneous Intermediates on Defect-Rich SnSSe/C Layered Heterostructure for Ultralong-Cycling Sodium Storage.

2D layered Sn-based materials have attracted enormous attention due to their remarkable performance in sodium-ion batteries. Nevertheless, this promising candidate involves a complex Na+ -storage process with multistep conversion-alloying reactions, which induces the uneven dispersion of heterogeneous intermediate accompanied by severe agglomeration of metallic Sn0 , inescapably resulting in poor reaction reversibility with sluggish rate capability and inferior cyclic lifespan. Herein, a delicately layered heterostructure SnSSe/C consisting of defect-rich SnSSe and graphene is designed and successfully achieved via a facile hydrothermal process. The equal anionic substitution of Se in SnSSe crystal can trigger numerous defects, which can not only facilitate Na+ diffusion but also accelerate the nucleation process by inducing quantum-dot-level uniform distribution of heterogeneous intermediates, Na2 Se/Na2 S and Sn0 . Concurrently, in situ formed uniform Na2 Se/Na2 S grain boundaries confined by this unique layered heterostructure may effectively suppress the agglomeration of metallic Sn0 nanograins and boost the reversibility of conversion-alloying reaction. As a result, the SnSSe/C displays significant improvement in Na-storage performance, in terms of remarkable rate capability and ultralong cycling lifespan. This work, focusing on controlling intermediate distribution, provides an effective strategy to boost reaction reversibility, which can be wildly employed in conversion-based electrodes for energy storage regions.

Observation of the Specific Heat Jump in the Se-Substituted MoTe2 Single Crystals

1T’-MoTe2 has gained considerable attention owing to its topological character. This material undergoes spatial inversion symmetry at 300 K. A structural transition to the Td phase, which is represented by a kink in the resistivity, was observed below 250 K without inversion symmetry along the c-axis, while superconductivity was observed at 0.1 K. Substitution of Se into this material suppressed the appearance of the kink structure and increased the superconducting transition temperature to 2 K, which is consistent with previously reported results on polycrystalline samples. However, a specific heat jump was observed in the obtained single crystals, which did not exhibit kink structures in their resistivity. The results suggest that the Td structure was not suppressed entirely after Se substitution and that superconductivity was achieved without inversion symmetry.

Selenium in Proteins: Conformational Changes Induced by Se Substitution on Methionine, as Studied in Isolated Model Peptides by Optical Spectroscopy and Quantum Chemistry.

The side-chain of methionine residues is long enough to establish NH⋯S H-bonds with neighboring carbonyl groups of the backbone, giving rise to so-called intra-residue 6δ and inter-residue 7δ H-bonds. The aim of the present article is to document how the substitution of sulfur with a selenium atom affects the H-bonding of the Met system. This was investigated both experimentally and theoretically by conformation-resolved optical spectroscopy, following an isolated molecule approach. The present work emphasizes the similarities of the Met and Sem residues in terms of conformational structures, energetics, NH⋯Se/S H-bond strength and NH stretch spectral shifts, but also reveals subtle behavior differences between them. It provides evidence for the sensitivity of the H-bonding network with the folding type of the Sem/Met side-chains, where a simple flip of the terminal part of the side-chain can induce an extra 50 cm−1 spectral shift of the NH stretch engaged in a 7δ NH⋯S/Se bond.

The dependence of the energy density states on the substitution of chemical elements in the Se6Te4-xSbx thin film

The energy density state are the powerful factor for evaluate the validity of a material in any application. This research focused on examining the electrical properties of the Se6Te4- xSbx glass semiconductor with x=1, 2 and 3, using the thermal evaporation technique. D.C electrical conductivity was used by determine the current, voltage and temperatures, where the electrical conductivity was studied as a function of temperature and the mechanical electrical conduction were determined in the different conduction regions (the extended and localized area and at the Fermi level). In addition, the density of the energy states in these regions is calculated using the mathematical equations. The constants of energy density states are determined, namely the electron hopping distance, the width of the tails, and pre - exponential factor. The densities of the energetic states (extended N (Eext), localize N (Eloc) and at the Fermi states N (Ef) will be calculated in each of the regions. Moreover, the effect of partial substitution of Se with antimony on energy states and degree of randomness, results observed that the energy densities changing with an increase antimony Sb concentration.

Efficient Oxygen‐Vacancy Suppression and Electrical Stabilization of Solution‐Processed In2O3:Q (Q = S, Se) Thin‐Film Transistor with Chalcogen Alloying

AbstractTransparent oxide semiconductors are successfully implemented as thin‐film transistors (TFTs) for large‐area display applications with superior electrical performance in comparison with that of conventional amorphous silicon. However, further development of high‐performance oxide semiconductors is hindered by the trade‐off between mobility and stability. Mixed metal composition containing heavy metal cations shows high‐mobility/low‐stability and light metal cations exhibits low‐mobility/high‐stability. A novel material design strategy for realizing a high‐performance oxide semiconductor for TFTs through partial substitution of Se or S for O in In2O3 is reported. In contrast to the conventional small‐sized Ga substitution for suppressing oxygen vacancies, the replacement of O by Se or S results in lattice stabilization and oxygen‐vacancy suppression, consequently stabilizing Se‐ or S‐incorporated In2O3 TFTs. In2O3:Se TFTs exhibit an average field‐effect mobility of 6.1 cm2 V−1s−1, ON/OFF current ratio (Ion/Ioff) of 108, and excellent operational stability with threshold voltage shift values of &lt;0.10 V at a positive and negative bias stress for 10 000 s. Furthermore, the seven‐stage ring oscillator circuit operating at a supply bias of 20 V exhibits an oscillation frequency of &gt;805 kHz and a corresponding propagation delay of &lt;90 ns per stage.

Synthesis and characterization of Ge-Ag-Sb-S-Se-Te high-entropy thermoelectric alloys

Multielement alloying is an appealing approach for suppressing thermal conductivity of thermoelectric materials. In this study, we synthesized GeTe-based high-entropy alloys with notable (S, Se) substitution at Te sites and (Ag, Sb) at Ge sites. The Ge0.82Ag0.08Sb0.1S0.5Se0.1Te0.4 exhibits an extremely low thermal conductivity of ∼ 0.66 W/m⋅K and a high Seebeck coefficient (>250 μV/K) over a temperature range of 150 – 400 °C. The influence of lattice distortion on phase transformation and transport properties of Ge0.9-2xAg2xSb0.1S0.5Se0.1Te0.4 (x = 0 – 0.06) was investigated.

Calcium hafnate perovskite from an insulator to a semiconductor for photovoltaic and photocatalytic hydrogen production from water splitting applications

Converting solar energy into electrical or chemical energy is an effective solution to produce clean and less expensive energy. Based on this, this paper sheds new light on the neglected photovoltaic and photocatalytic hydrogen production from water splitting applications of lead-free calcium hafnate perovskite (CHO) by converting CHO from an insulator to a semiconductor by doping CHO with chalcogens. Moreover, the intrinsic oxygen vacancy (Vo) defect in oxide materials was taken into consideration in our calculations based on DFT using LDA + mBJ approximation. It was found that when CHO was doped with chalcogens impurities the forbidden band was decreased with the increase of chalcogens impurities concentrations in CHO, especially when Tellurium (Te) and Selenium (Se) substitutions meet a Vo defect in CHO due to the increases to its charge carries' mobility. Furthermore, when chalcogens impurities meet a Vo defect in CHO the edge's absorption extends in the visible spectrum which is a basic requirement for photovoltaic and photocatalyst devices.

Selenium migration mechanism in wet FGD slurry: Experimental and DFT analysis

Selenium (Se) is one of the hazardous trace elements emitted from coal-fired power plants. The Se migration behavior in wet flue gas desulfurization (FGD) slurry is still unclear, and the species of Se in FGD gypsum remains controversial. In this research, the bubbling experiments using simulated slurry with/without gypsum crystallization process were conducted. The experimental results indicated that pure gypsum has poor capability to capture Se components, and only selenite could be trapped in gypsum during its crystal growth stage. Furthermore, the DFT calculation was conducted to provide the microscopic information of Se adsorption and substitution characteristics during gypsum crystallization process. The research findings of this study could help understand the mechanism of Se migration process in FGD slurry, and facilitate the development of effective Se emission control technologies in the future.