Molybdenum Atoms Research Articles

FORMATION AND DECOMPOSITION OF ANOMALOUS SUPERSATURATED MOLYBDENUM SOLUTIONS IN COPPER-BASED CONDENSATES


 Cu-Mo condensates in the concentration range of the latter from 0.3 to 1.5 at.%, obtained by simultaneous evaporation in vacuum with subsequent condensation of the resulting vapor mixture on a non-orienting substrate (PVD method), were studied. The components of this system do not form chemical compounds under equilibrium conditions and are mutually insoluble in liquid and solid states. The structure of Cu-Mo condensates was studied by transmission electron microscopy and X-ray diffractometry both in the derivative state and after a series of isothermal anneals in the temperature range from 300 to 900°C. It was found that small concentrations of molybdenum lead to significant dispersion of the matrix metal. Molybdenum tends to form segregations at the boundaries of copper grains and form a strong coherent bond with the matrix metal, which persists even after isothermal annealing. The conditions for the formation of an anomalous supersaturated solid solution of molybdenum in the copper matrix, as well as the conditions for its decomposition, have been revealed. An assumption is made about the mechanism of formation of such a solution during condensation from the vapor phase, which consists in the kinetic capture of molybdenum atoms by the crystallization front during condensation from the vapor phase. It was found that the decomposition of the supersaturated solid solution begins when heated to 0.5 of the melting point of copper and is accompanied by a dispersion solidification process. During the experiment, it was first recorded that the dispersion solidification process can have a two-stage character. The first peak is observed in the region of 30 minutes of annealing, and the second peak is observed after about 2 hours of isothermal annealing. The height of the dispersion hardening peaks increases with increasing molybdenum concentration. It is suggested that the appearance of the second peak of dispersion hardening is associated with the peculiarities of the interaction between copper grains and molybdenum segregations at the grain boundaries. It is shown that the structure after solution decomposition is typically composite. The advantage of this material over conventional dispersively hardening alloys is the fact that in these pseudo-alloys there is no reverse solution of hardening particles at an increase in temperature.

Occurrence state and enrichment mechanism of rhenium in molybdenite from Merlin Deposit, Australia

Rhenium (Re) is one of the critical metals, and molybdenite (MoS2) is the main host mineral for Re. Previous studies have shown that the distribution of Re in molybdenite is highly heterogeneous, and the occurrence state and enrichment mechanism of Re in molybdenite is not clear. The molybdenite of Merlin deposit has typical Re rich characteristics, which is an ideal object to study the occurrence state and enrichment mechanism of Re in molybdenite. Based on the geological research of the deposit, this study systematically investigated the Re-rich molybdenite of the Merlin deposit using LA-ICP-MS and STEM techniques. The LA-ICP-MS results showed that the content of Re in molybdenite ranged from 67 to 2726 ppm, and the distribution of Re content in molybdenite was extremely uneven and irregular. The STEM results showed that there was no independent Re mineral in molybdenite, and Re atoms were found to substitute molybdenum (Mo) atoms in situ in the Re-rich area of molybdenite. The substitution mechanism of Re was clarified at the atomic scale in a visual form, and a corresponding rigid sphere stacking model was established. Mo atoms are sandwiched between two layers of S atoms, while Re atoms enter the molybdenite lattice and substitute Mo atoms in situ, thus changing the lattice structure of the original molybdenite matrix. Rare lattice defects such as five-fold twinning were identified in the Re-rich area of molybdenite in high-resolution HAADF STEM images, which are related to plastic deformation caused by the low stacking fault energy and stress of hexagonal molybdenite. It is speculated that lattice defects such as five-fold twinning is an important mechanism for the enrichment of Re in molybdenite. The magmatic-hydrothermal fluids released from the intrusion of igneous rocks may have provided the main source of ore-forming materials for the Merlin deposit. The ore-forming fluids, which are rich in Mo4+ and Re4+, underwent redox reactions with carbonaceous shale, resulting in the decrease in temperature and oxygen fugacity, and the increase in S2- concentration. This ultimately led to the precipitation and enrichment of Re4+ and Mo4+ to form the Re-rich molybdenite in the Merlin deposit.

Stable Janus monolayer MoSHx (0.5 ≤ x ≤ 2)

MoSH is a representative example of a Janus two-dimensional monolayered system consisting of a molybdenum atomic layer sandwiched between sulfur and hydrogen atomic layers. Extensive experimental and theoretical efforts have suggested the great promise of the MoSH material, but the validity of the MoSH model (with a Mo–S–H ratio of 1:1:1) remains uncertain. While various experiments have established the Mo-to-S ratio to be close to 1:1, the hydrogen content has remained elusive even with the use of state-of-the-art characterization techniques due to its lightweight nature. In this study, we present a theoretical investigation aiming to determine the positions and ratios of the hydrogen atoms on MoSHx (with x ranging from 0 to 3) as well as assess their structural stability. By evaluating the energetic, mechanical, and thermodynamic properties, we confirm the existence of stable MoSHx structures within a critical range of hydrogen atom ratios, specifically 0.5 ≤ x ≤ 2.0. Additionally, as the hydrogen atom ratio increases, we observe a transition in the preferred adsorption sites of hydrogen atoms from the center of the hexagonal ring composed of molybdenum and sulfur atoms to the upper region of the molybdenum atoms. This study offers critical insight into the structural characteristics and stability of Janus monolayer MoSHx, contributing to the advancement and application of Janus MoSHx in various fields.

Tetra-μ3-selen-ido-1:2:3κ3Se;1:2:4κ3Se;1:3:4κ3Se;2:3:4κ3Se-tetrakis-[(η5-methyl-cyclo-penta-dien-yl)molybdenum(III)](6 Mo-Mo).

The title cluster compound, [Mo4(η5-C5H4Me)4(μ3-Se)4], was synthesized from the reaction of [Mo(η5-C5H4Me)(CO)3]2 with grey selenium in refluxing xylene solution under a nitro-gen atmosphere. The complete cluster is generated by a crystallographic twofold axis and contains an Mo4Se4 cubane-like core surrounded by four η5-methylcyclo-pentadienyl ligands. In the core, the four molybdenum atoms are connected to each other to form a tetra-hedron, with a selenium atom capping each face. The Mo-Mo bond lengths vary from 2.9857 (5) to 3.0083 (3) Å and the Mo-Se separations range from 2.4633 (4) to 2.4693 (5) Å.

Catalytic Activity of Molybdenum Complexes Bearing PNP-Type Pincer Ligand toward Ammonia Formation.

We newly designed and prepared a novel molybdenum complex bearing a 4-[3,5-bis(trifluoromethyl)phenyl]pyridine-based PNP-type pincer ligand, based on the bond dissociation free energies (BDFEs) of the N-H bonds in molybdenum-imide complexes bearing various substituted pyridine-based PNP-type pincer ligands. The complex worked as an excellent catalyst toward ammonia formation from the reaction of an atmospheric pressure of dinitrogen with samarium diiodide as a reductant and water as a proton source under ambient reaction conditions, where up to 3580 equivalents of ammonia were formed based on the molybdenum atom of the catalyst. The catalytic activity was significantly improved by one order of magnitude larger than that observed when using the complex before modification.

Catalytic Activity of Molybdenum Complexes Bearing PNP‐Type Pincer Ligand toward Ammonia Formation

AbstractWe newly designed and prepared a novel molybdenum complex bearing a 4‐[3,5‐bis(trifluoromethyl)phenyl]pyridine‐based PNP‐type pincer ligand, based on the bond dissociation free energies (BDFEs) of the N−H bonds in molybdenum‐imide complexes bearing various substituted pyridine‐based PNP‐type pincer ligands. The complex worked as an excellent catalyst toward ammonia formation from the reaction of an atmospheric pressure of dinitrogen with samarium diiodide as a reductant and water as a proton source under ambient reaction conditions, where up to 3580 equivalents of ammonia were formed based on the molybdenum atom of the catalyst. The catalytic activity was significantly improved by one order of magnitude larger than that observed when using the complex before modification.

Electrocatalysts for Zinc-Air Batteries Featuring Single Molybdenum Atoms in a Nitrogen-Doped Carbon Framework.

Bifunctional catalysts can facilitate two different electrochemical reactions with conflicting characteristics. Here, a highly reversible bifunctional electrocatalyst for rechargeable zinc-air batteries (ZABs) is reported featuring a "core-shell structure" in which N-doped graphene sheets wrap around vanadium molybdenum oxynitride nanoparticles. Single Mo atoms are released from the particle core during synthesis and anchored to electronegative N-dopant species in the graphitic shell. The resultant Mo single-atom catalysts excel as active oxygen evolution reaction (OER) sites in pyrrolic-N and as active oxygen reduction reaction (ORR) sites in pyridinic-N environments. ZABs with such bifunctional and multicomponent single-atom catalysts deliver high power density (≈376.4mWcm-2 ) and long cycle life of over 630h, outperforming noble-metal-based benchmarks. Flexible ZABs that can tolerate a wide range of temperatures (-20 to 80°C) under severe mechanical deformation are also demonstrated.

Mechanical properties and corrosion behavior in molten zinc of Mo–ZrO2 alloys

The effect of the ZrO2 doping amounts on the corrosion properties and mechanical properties of the molybdenum alloys in molten zinc was investigated. Among them, the Mo-1.5 wt% ZrO2 alloy has good corrosion resistance (at 460 °C) and excellent mechanical properties. Compared with that of pure molybdenum, the tensile strength of the Mo-1.5 wt%ZrO2 increased by 16.69% in the rotary forged state and 58.26% in the 1200 °C annealed states, and the compressive strength increased by 16.53% and 84.46%, respectively. At a corrosion temperature of 460 °C, a MoZn7 corrosion layer was formed, which isolates the molybdenum matrix from direct contact with the molten zinc. The distribution of ZrO2 particles in the corrosion layer, which changes the diffusion path of zinc and molybdenum atoms, thus slowing down the corrosion process. The thickness of the corrosion layer gradually decreases with increasing doping amount, where the corrosion layer thickness of the Mo-2.0 wt% ZrO2 is 45.21% lower than that of the pure molybdenum. At a corrosion temperature of 560 °C, the molybdenum matrix is exposed to molten zinc and the grains peel off. As the bond between Mo grains is better than the bond between Mo grains and zirconia, the grain spalling of the zirconia-doped molybdenum alloys is severer than that of pure molybdenum.

Ternary transition metal of Fe/Co/Ni doping on MoSx nanowires for highly efficient electrochemical oxygen evolution

The crucial step for splitting water is the oxygen evolution reaction. The key to promote this reaction lies in the catalyst. Molybdenum disulfide, as a two-dimensional material with molybdenum and sulfur atoms stacked, is especially suitable as a doping platform to develop high-performance OER catalysts. Fe/Co/Ni ternary transition metal combination has always been a highly active catalytic site for OER. Heteroelement of Fe/Co/Ni doping is expected to effectively modify the local electronic configuration of matrix materials and thus enhances their electrocatalytic OER capability. With this in mind, we report a simple in-situ hydrothermal doping of MoSx nanowires on iron‑nickel alloy foam with ternary transition metal of Fe/Co/Ni. This ternary transition metal of Fe/Co/Ni doped f self-supported electrode (denoted Fe/Co/Ni-MoSx/INF) displays outstanding OER performance in terms of small overpotentials of 214 and 263 mV at current densities of 10 and 100 mA/cm2, respectively, in alkaline solution. It was far better than the commercial Ir/C catalysts (253 and 434 mV@10 and 100 mA/cm2). The Tafel slope is about 48.1 mV/dec. Moreover, Fe/Co/Ni-MoSx/INF also has an excellent catalytic stability without any obvious performance decay after 20 h operation. This work contributes to the investigation of high-efficiency OER catalysts based on transition metal-doped MoSx and offers a substitute for noble metal catalysts.

Effect of Al2O3 particles on the corrosion behavior of molybdenum alloys in molten zinc

A new method that samples and a certain amount of Zn grains are sealed into a quartz tube under vacuum is designed to investigate the corrosion behavior of molybdenum alloys in molten zinc, with the mechanism of action of Al2O3 investigated. The molybdenum alloys annealed at 1200 ℃ exhibit an excellent corrosion resistance to liquid zinc. After 40 days of corrosion, the corrosion rate of Mo-2.0 wt%Al2O3 decreased by 47.92 % compared with that of pure molybdenum. Al2O3 particles distributing in the matrix and corrosion layer can change the diffusion path of molybdenum and zinc atoms, improving the corrosion resistance of molybdenum alloys.

Molybdenum Atom Engineered Vanadium Disulfide for Boosted High-Capacity Li-Ion Storage.

A drawback with lithium-ion batteries (LIBs) lies in the unstable lithium storage which results in poor electrochemical performance. Therefore, it's of importance to improve the electrochemical functionality and Li-ion transport kinetics of electrode materials for high-performance lithium storage. Here, a subtle atom engineering via injecting molybdenum (Mo) atoms into vanadium disulfide (VS2 ) to boost high capacity Li-ion storage is reported. By combining operando, ex situ monitoring and theoretical simulation, it is confirmed that the 5.0%Mo atoms impart flower-like VS2 with expanded interplanar spacing, lowered Li-ion diffusion energy barrier, and increased Li-ion adsorption property, together with enhanced e- conductivity, to boost Li-ion migration. A "speculatively" optimized 5.0% Mo-VS2 cathode that exhibits a specific capacity of 260.8mA h g-1 at 1.0 A g-1 together with a low decay of 0.009% per cycle over 500 cycles is demonstrated. It is shown that this value is ≈1.5 times compared with that for bare VS2 cathode. This investigation has substantiated the Mo atom doping can effectively guide the Li-ion storage and open new frontiers for exploiting high-performance transition metal dichalcogenides for LIBs.

Synthesis and characterization of volatile liquid Mo precursors for vapor phase deposition of thin films containing molybdenum

Volatile molybdenum precursors in liquid phase for vapor phase deposition of thin films containing molybdenum have been successfully synthesized. Heteroleptic liquid molybdenum precursors were prepared by treating MoCl5 with bidentate β-ketonate ligands such as 2,2,6,6-Tetramethyl-3,5-heptanedione (thdH) at different stoichiometric ratios (1:1 and 1:2). Molybdenum precursors in liquid phases also have been obtained via simple ligand-exchange reactions of Mo(thd)xCl4-x (x = 1 or 2) with LiNR2 (R = Et(C2H5), iPr(C3H7), SiMe3(Si(CH3)3)). The newly synthesized molybdenum precursors are readily miscible (soluble) in most organic solvents, such as acetonitrile, diethyl ether, and hexane. The chemical composition of these precursors has been characterized using Fourier-transform infrared analysis and nuclear magnetic resonance spectroscopy. The volatility and thermal stability of precursor compounds have also been investigated using thermogravimetric analysis and vapor pressure measurement. The strategy used in this experiment, which introduces bidentate ligands to the coordination sphere of the central molybdenum atom in MoCl5, improves the volatility and transferability of molybdenum precursors in gas-phase deposition processes by making them in a liquid phase.

Catalytic production of ammonia from dinitrogen employing molybdenum complexes bearing N-heterocyclic carbene-based PCP-type pincer ligands

Mechanistic insight into the catalytic production of ammonia from dinitrogen is needed to improve the synthesis of this vital molecule. Here we study the use of samarium diiodide (SmI2) and water in the presence of molybdenum complexes that bear PCP-type pincer ligands to synthesize ammonia. The proton-coupled electron transfer during the formation of a N–H bond on the molybdenum imide complex was found to be the rate-determining step at high catalyst concentrations. Additionally, the dimerization step of the catalyst became the rate-determining step at low catalyst concentrations. We designed PCP-type pincer ligands with various substituents at the 5- and 6-positions and observed that electron-withdrawing groups promoted the reaction rate, as predicted by density functional theory calculations. A molybdenum trichloride complex that bears a trifluoromethyl group functioned as the most effective catalyst and produced up to 60,000 equiv. ammonia based on the molybdenum atom of the catalyst, with a molybdenum turnover frequency of up to 800 equiv. min−1. The findings reported here can contribute to the development of an environmentally friendly next-generation nitrogen-fixation system.

КИСЛОРОД-ИОННАЯ ПРОВОДИМОСТЬ В СОЕДИНЕНИЯХ СО СТРУКТУРОЙ ТИПА ГОЛЛАНДИТА LnMo6O12 (Ln = Pr, Nd)

The results of the study of oxygen ion diffusion paths in the structures of PrMo6O12 and NdMo6O12 compounds having a hollandite type structure using a complex theoretical approach, including GT analysis, BVSE method,and DFT modeling, are presented. It is shown that the migration of O2- ions occurs along a one-dimensional system of channels, diffusion along transitions located between the atoms of praseodymium and molybdenum is predominant. The energy barriers of the transitions exceed 1.23 eV, therefore, oxygen-ion conductivity at room temperature is difficult.

Ultrafast electron localization and screening in a transition metal dichalcogenide

The coupling of light to electrical charge carriers in semiconductors is the foundation of many technological applications. Attosecond transient absorption spectroscopy measures simultaneously how excited electrons and the vacancies they leave behind dynamically react to the applied optical fields. In compound semiconductors, these dynamics can be probed via any of their atomic constituents with core-level transitions into valence and conduction band. Typically, the atomic species forming the compound contribute comparably to the relevant electronic properties of the material. One therefore expects to observe similar dynamics, irrespective of the choice of atomic species via which it is probed. Here, we show in the two-dimensional transition metal dichalcogenide semiconductor MoSe2, that through a selenium-based core-level transition we observe charge carriers acting independently from each other, while when probed through molybdenum, the collective, many-body motion of the carriers dominates. Such unexpectedly contrasting behavior can be explained by a strong localization of electrons around molybdenum atoms following absorption of light, which modifies the local fields acting on the carriers. We show that similar behavior in elemental titanium metal [M. Volkov et al., Nat. Phys. 15, 1145-1149 (2019)]carries over to transition metal-containing compounds and is expected to play an essential role for a wide range of such materials. Knowledge of independent particle and collective response is essential for fully understanding these materials.

Effect of intercalated molybdenum atoms on structure and electrochemical properties of Mo1+x S2 synthesized by hydrothermal method

As an alternative anode to graphene, molybdenum disulfide (MoS2) has attracted much attention due to its layered structure and high specific capacity. Moreover, MoS2 can be synthesized by hydrothermal method with low cost and the size of its layer spacing can be controlled. In this work, the results of experiment and calculation proved that the presence of intercalated Mo atoms, leading to the expansion of MoS2 layer spacing and weakening of Mo–S bonding. For the electrochemical properties, the presence of intercalated Mo atoms causes the lower reduction potentials for the Li+ intercalation and Li2S formation. In addition, the effective reduction of diffusion resistance and charge transfer resistance in Mo1+x S2 leads to the acquisition of high specific capacity for battery applications.

CRYSTAL AND MOLECULAR STRUCTURE OF THE ISLAND TETRANUCLEAR DIOXOMOLYBDENUM(VI) COMPLEX [MoO<sub>2</sub>(<i>L</i><sup>1</sup>)]<sub>4</sub> (H<sub>2</sub><i>L</i><sup>1</sup> IS ACETYLACETONE ISONICOTINOYLHYDRAZONE) WITH LARGE INTRA- AND INTERMOLECULAR CHANNELS

The solvated complex [МоО2(L1)]4dimethylformamide (I) was synthesized. Its structure wasdetermined by X-ray diffraction analysis. The crystal structure is composed of the tetranuclear complexes [МоО2(L1)]4 (Ia) as the structural units lying on crystallographic twofold axes. Both crystallographically independent molybdenum atoms are in a distorted octahedral coordination environment formed by two cis-О(oxo) ligands, two N(L1) atoms of two molecules Ia in trans positions to the О(oxo) ligands, and two О(L1) atoms of one complex molecule in cis positions to О(oxo) and trans to each other. Each (L1)2– ligand is coordinated to two Мо atoms in a tetradentate tridentate-chelating (2О, N) bridging (N) mode. The average bond lengths in complex Iа are as follows: Мо–О(oxo), 1.701 Å; Мо–N(L1), 2.460 (b) and 2.214 Å (c); Мо–О(L1), 1.980 Å. The О(oxo)–МоО–(oxo) bond angle is 105.6°. The ordered dimethylformamide molecule is located in a narrow channel in the structure. The strongly disordered (non-located) solvent molecules (methanol/dimethylformamide/water) occupy wide channels in the structure of I.

Laser-enabled localized synthesis of Mo1-xWxS2 alloys with tunable composition

Alloying can tailor the optoelectronic properties of two-dimensional transition metal dichalcogenides (2D-TMDC) by bandgap tuning and shallowing of the deep-level defects, leading to enhancement in their photodetection performance. Hence, seeking for a scalable composition-controlled alloy preparation technology is essential. Here, direct laser-synthesis of micro-patterned Mo1-xWxS2 alloys is demonstrated. By irradiating composite single source precursor films of molybdenum and tungsten sulfides with a laser beam at visible wavelengths, photo-thermal decomposition takes place, thus forming high-quality Mo1-xWxS2 alloys in ambient conditions without any need for high-vacuum based environment. The Mo1-xWxS2 alloys composition is simply regulated by adjusting the volume ratio of the partial single source precursor solutions, in the final mixture solution.The stoichiometry, the structural, morphological and optical characteristics of laser-written alloys with different compositions have been investigated. Analysis of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed the formation of the long-range (∼30 nm), few-layered crystals with randomly distributed molybdenum and tungsten metal atoms with no evidence of clustering. A photosensing device has been fabricated from laser-written Mo0·5W0·5S2 alloys to demonstrate the functionality of the material.

MoxWx–1S2 Nanotubes for Advanced Field Emission Application

AbstractTransition metal dichalcogenide (TMDC) nanotubes complement the field of low‐dimensional materials with their quasi‐1D morphology and a wide set of intriguing properties. By introducing different transition metals into the crystal structure, their properties can be tailored for specific purpose and applications. Herein, the characterization and a subsequent preparation of single‐nanotube field emission devices of MoxWx‐1S2 nanotubes prepared via the chemical vapor transport reaction is presented. Energy‐dispersive X‐ray spectroscopy, Raman spectroscopy, and X‐ray diffraction indicate that the molybdenum and tungsten atoms are randomly distributed within the crystal structure and that the material is highly crystalline. High resolution transmission electron microscopy and electron diffraction (ED) patterns further corroborate these findings. A detailed analysis of the ED patterns from an eight‐layer nanotube reveal that the nanotubes grow in the 2H structure, with each shell consists of one bilayer. The work function of the nanotubes is comparable to that of pure MoS2 and lower of pure WS2 NTs, making them ideal candidates for field emission applications. Two devices with different geometrical setup are prepared and tested as field emitters, showing promising results for single nanotube field emission applications.

Структура и свойства биоинертного покрытия Mo – Nb, сформированного на медицинском сплаве Titanium Grade 5 электровзрывным методом

In this article, an attempt was made to solve the problem of creating a coating for an implant that has better biological compatibility than the medical titanium alloy Titanium Grade 5. A Mo – Nb coating of the composition Mo – Nb is formed on the titanium grade 5 medical alloy by the electroexplosive method. The coating is formed as a result of the simultaneous electric explosion of molybdenum and niobium foils. A set of studies has been carried out to establish the structure, phase composition, and properties of the formed coatings. The coatings were studied by scanning and transmission electron microscopy. It is shown that the hardness of the surface layer of the coating by 60 % and Young’s modulus by 43 % exceed the corresponding characteristics of the Titanium Grade 5 alloy. The thickness of the layer with high (relative to the substrate) values of hardness and Young’s modulus reaches 80 µm. It was found that the wear parameter of the coating is 1.8 times, and the friction coefficient of the coating is 1.6 times higher than the wear parameter and the friction coefficient of the substrate. It has been established that in the surface layer, along with the coating atoms, there are Al, Ti, V atoms, which indicates that the coating is doped with substrate atoms, as well as oxygen and carbon atoms. The layering of the coating by elemental composition was revealed, namely, the top of the coating is enriched with niobium atoms, the lower part of the coating is enriched with molybdenum atoms. It is shown that the coating has a polycrystalline structure formed by a solid solution based on molybdenum. In the bulk and along the grain boundaries, there are inclusions of the second phase of the composition a-Ti, Nb, Mo9Ti4, and NbTi4 of various shapes and sizes. The studies of the phase composition did not reveal compounds based on vanadium and aluminum, which reduce the biocompatibility of the coatings. The identified phases contain only molybdenum, niobium and titanium, which are bioinert. This fact suggests that, as in studies of the phase composition of the surface of the coatings and its change in thickness, the biocompatibility of the obtained coatings will be higher compared to the Titanium Grade 5 titanium alloy. The conducted complex of studies makes it possible to recommend the resulting coatings for further clinical trials. These coatings are expected to be used in the future for better survival of titanium implants in the human body.