Chemical Vapor Transport Reaction Research Articles

Bulk ferromagnetism in cleavable van der Waals telluride NbFeTe2.

A van der Waals telluride, NbFeTe2, has been synthesized using chemical vapor transport reactions. The optimized synthetic conditions yield high-quality single crystals with a novel monoclinic crystal structure. Monoclinic NbFeTe2 demonstrates a (100) cleavage plane, bulk ferromagnetism below 87 K, and a metallic ground state-the necessary prerequisites for needed spintronics technologies.

Polyoxometalates from gases: Mineral-inspired synthesis and characterization of novel compounds containing [M⊂Cu12O8(AsO4)8]q- polyoxocuprate clusters (M = Ti(IV), Bi(III))

A novel type of polyoxocuprate (POCu) clusters, [M⊂Cu12O8(AsO4)8]q- (M = Ti(IV), Bi(III)), with a cubooctahedral arrangement of Cu2+ cations, have been prepared by chemical vapor transport reactions (CVT) using the methodology inspired by mineralogical discoveries at volcanic fumaroles of the Tolbachik volcano (Kamchatka peninsula, Russia). Three new compounds, Na21Cl6F[TiF6][TiCu12O8(AsO4)8] (1), Na18Cl6[TiCu12O8(AsO4)8] (2), and Na18Cl5[BiCu12O8(AsO4)8] (3), prepared under low-vacuum conditions, contain the {[M⊂Cu12O8](AsO4)8} (M = Ti4+, Fe3+) clusters with a Keggin-ion-like cubooctahedral arrangement of Cu2+ cations encapsulating Mn+ cations strikingly similar to the {[Pd13O8]L8]q- polyoxoanions observed in polyoxopalladates. The packing modes of clusters in different structures are different, with the structures of 1 and 3 based upon cubic-close-packing and hexagonal-close-packing arrangements, respectively. The packing of clusters in 2 is rather complex that results in its extreme structural complexity with the amount of Shannon structural information per unit cell exceeding 3000 bits. In the title compounds, the POCu clusters are embedded into salt matrices and therefore can be considered as an inverse analogue of salt-inclusion compounds, i.e., as inclusion-in-salt compounds. The successful synthesis of new types of POCu clusters using the CVT techniques opens up a new synthetic pathway for the exploration of polyoxocuprates with promising interesting structures and physical properties.

Synthesis and Formulation of Ternary Transition Metal Dichalcogenide Alloys for Additive Electronic Manufacturing

Compared with the most investigated graphene, layered transition metal dichalcogenides (TMDs) have received significant attention due to their various chemical compositions and great potential electronic application. In order to tailor and engineer properties of TMDs and therefore enhance their efficiency toward commercial applications, several methods have been employed including reducing dimensionality, creating inter and intra-heterostructures, introducing inter stain, and alloying. Among these, alloying via chemical vapor transport (CVT) is scalable, cost- efficient, and controllable method of tuning TMD bulk crystal properties. Alloying of TMDs can be categorized into several types including metal replacement, dichalcogenide replacement, and both metal and dichalcogenide replacement. In a typical TMD CVT reaction, high-purity precursors are mixed in a desired stochiometric ratio, vacuumed, and sealed in an ampoule to form a closed system. The resulting TMD crystal can then be used for additional processes, e.g., exfoliation to yield 2D TMD nanosheets. Additive electronics manufacturing is a promising technique for the scalable fabrication of electronic devices, including sensors and energy storage devices. For an ink to be compatible for different printing modalities the ink rheology including viscosity, surface tension, and solid requires to be tuned to obtain suitable fluid dynamic parameters for jetting the ink. This work summarizes the development, synthesis, characterization, and formulation of two-dimensional ternary TMDCs ink for aerosol jet printing (AJP) technology. Ball milling assisted liquid exfoliation is utilized for synthesizing ternary TMDs nanomaterials under controlled condition. The resulting nanomaterial is developed into nanomaterial ink compatible with AJP. Detailed analysis of the material characterization and ink properties are required to optimize the fluid dynamics and properties of the ink. After printing the formulated ink using AJP on various substrates, post-printing process techniques is required to be investigated for printed nanomaterials inks to achieve bulk-like performance for the printed structures. Our results highlight the innovations in synthesis and formulation of ternary transition metal dichalcogenide nanomaterial inks for additive manufacturing of electronic devices such as sensors, solar cells, and energy storage devices.

Polarization conversion in bottom-up grown quasi-1D fibrous red phosphorus flakes

Fibrous red phosphorus (RP) has triggered growing attention as an emerging quasi-one-dimensional (quasi-1D) van der Waals crystal recently. Unfortunately, it is difficult to achieve substrate growth of high-quality fibrous RP flakes due to their inherent quasi-1D structure, which impedes their fundamental property exploration and device integration. Herein, we demonstrate a bottom-up approach for the growth of fibrous RP flakes with (001)-preferred orientation via a chemical vapor transport (CVT) reaction in the P/Sn/I2 system. The formation of fibrous RP flakes can be attributed to the synergistic effect of Sn-mediated P4 partial pressure and the SnI2 capping layer-directed growth. Moreover, we investigate the optical anisotropy of the as-grown flakes, demonstrating their potential application as micro phase retarders in polarization conversion. Our developed bottom-up approach lays the foundation for studying the anisotropy and device integration of fibrous red phosphorus, opening up possibilities for the two-dimensional growth of quasi-1D van der Waals materials.

CrB-type, ordered α-MnB: Single crystal structure and spin-canted magnetic behavior

Manganese monoboride has a low- (α) and a high-temperature (β) modification, as well as a defect-rich low-temperature variant (α′). The crystal structure (FeB-type structure, s.g. Pnma) and properties of high-temperature MnB are well-known. In this work, single crystals were grown via chemical vapor transport reactions, both of β-MnB and the low-temperature modification, α-MnB. This allowed for determining the crystal structure of defect-free α-MnB [CrB-type structure, s.g. Cmcm, a = 3.0098(6) Å, b = 7.6390(2) Å, and c = 2.94620(6) Å]. Furthermore, α′-MnB, the stacking fault-dominated CrB-variant, was obtained as crystalline powder and characterized by X-ray powder diffraction and transmission electron microscopy. Direction-resolved measurements of the magnetic properties of α-MnB revealed spin-canted magnetic behavior along c and ferromagnetism along a and b with a Curie temperature of 456 K; ferromagnetic β-MnB has a Curie temperature of 568 K.

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.

Cleavable crystals, crystal structure, and magnetic properties of the NbFe1+xTe3 layered van der Waals telluride.

Transition metal-based two-dimensional nanomaterials with competing magnetic states are at the cutting edge of spintronic and low-power memory devices. In this paper, we present a Fe-rich NbFe1+xTe3 layered telluride (x ≈ 0.5), which shows an interplay of spin-glass and antiferromagnetic states below the Néel temperature of 179 K. The compound has a layered crystal structure, where the NbFeTe3 layers are terminated by the Te atoms and van der Waals gaps. Bulk single crystals grown by chemical vapor transport reactions possess the (1̄01) cleavage plane suitable for the exfoliation of two-dimensional nanomaterials. Combination of high-resolution transmission electron microscopy and powder X-ray diffraction reveals the zigzag ladders of Fe atoms inside the structural layers, as well as complementary zigzag chains of the partially occupied Fe positions in the interstitial region. Fe atoms carry large effective magnetic moment of 4.85(3)μB per atom in the paramagnetic state yielding intriguing magnetic properties of NbFe1+xTe3. They include frozen spin-glass state at low temperatures and spin-flop transition in high magnetic fields indicating promising flexibility of the magnetic system and its potential control by magnetic field or gate tuning in the spintronic devices and heterostructures.

Na2Cu+[Cu2+ 3O](AsO4)2Cl and Cu3[Cu3O]2(PO4)4Cl2: two new structure types based upon chains of oxocentered tetrahedra

Abstract Single crystals of Na2Cu+[Cu2+ 3O](AsO4)2Cl (1) and Cu3[Cu3O]2(PO4)4Cl2 (2) were prepared by chemical vapor transport reactions. Both crystal structures are based upon the same [O2Cu6]8+ chains formed by corner-sharing (OCu4)6+ tetrahedra and interconnected by (TO4)3− (T = P, As) tetrahedra into porous {[OCu3](TO4)2Cl}3− frameworks. The channels within the frameworks are occupied by Na+, Cu+ and Cl− ions in the crystal structure of 1, whereas the channels in the structure of 2 contain edge-sharing CuO4Cl tetragonal pyramids. Both compounds are structurally related to the previously described synthetic Na2Cu+[Cu2+ 3O](PO4)2Cl and NaCu2+[Cu2+ 3O](PO4)2Cl. The compound 2 is structurally and chemically related to yaroshevskite, Cu3[Cu3O]2(VO4)4Cl2, a mineral discovered in volcanic fumaroles, but the two structure types are drastically different. The crystal chemical analysis of the title and related compounds allows to recognize a family of at least four compounds based upon {[OCu3](TO4)2Cl}3− frameworks with channels occupied by different chemical constituents.

Fe-Rich Ferromagnetic Cleavable Van der Waals Telluride Fe5AsTe2

Transition metal-based layered compounds with van der Waals gaps between the structural layers are a rich source of magnetic materials for spintronic applications. Bulk crystals can be cleaved, providing high-quality two-dimensional nanomaterials, which are promising for the manipulation of spins in spintronic devices and low power quantum logic interfaces. The layered van der Waals telluride Fe5AsTe2 can be synthesized by the high-temperature reaction of elements. In the crystal structure, Fe-rich structural layers with the composition of Fe4.58(4)AsTe2 are separated by the van der Waals gaps with no atoms in the interstitial region. Crystal growth employing chemical vapor transport reactions yields bulk cleavable crystals, which exhibit weak inherent ferromagnetism below the Curie temperature of TC = 48 K. In the ordered state, the magnetization shows a dual-slope behavior in low magnetic fields, indicating the compensated or canted nature of magnetism. Magnetic susceptibility and magnetization measurements reveal perpendicular magnetic anisotropy. The large Rhodes-Wohlfarth ratio of 4.6 indicates the itinerant nature of ferromagnetism in Fe5AsTe2.

Influence of crystal structure and oxygen vacancies on optical properties of nanostructured multi-stoichiometric tungsten suboxides

Four distinct tungsten suboxide (WO3–x ) nanomaterials were synthesized via chemical vapour transport reaction and the role of their crystal structures on the optical properties was studied. These materials grow either as thin, quasi-2D crystals with the W n O3n-1 formula (in shape of platelets or nanotiles), or as nanowires (W5O14, W18O49). For the quasi-2D materials, the appearance of defect states gives rise to two indirect absorption edges. One is assigned to the regular bandgap occurring between the valence and the conduction band, while the second is a defect-induced band. While the bandgap values of platelets and nanotiles are in the upper range of the reported values for the suboxides, the nanowires’ bandgaps are lower due to the higher number of free charge carriers. Both types of nanowires sustain localized surface plasmon resonances, as evidenced from the extinction measurements, whereas the quasi-2D materials exhibit excitonic transitions. All four materials have photoluminescence emission peaks in the UV region. The interplay of the crystal structure, oxygen vacancies and shape can result in changes in optical behaviour, and the understanding of these effects could enable intentional tuning of selected properties.

Deposition of nano-crystalline tungsten carbide powders from gaseous WO2(OH)2

Lower WC grain sizes in the nanometer range have positive effects on the properties of hardmetals (e.g., hardness), but the established production processes of WC are limited to grain sizes of about 150 nm. To produce WC powder with grain sizes in the lower nanometer range, an alternative WC production process based on the chemical vapor transport (CVT) reaction of WO3 and H2O forming gaseous WO2(OH)2 at about 1100 °C, followed by a carburation reaction with H2/CH4-gas mixtures was investigated. The influences of different process parameters such as furnace temperature, humidity and gas flows were investigated to improve the process. With the right set of parameters the produced powder consisted mainly of agglomerated WC grains with a size of about 5 nm. Beside the common hexagonal WC phase, the cubic WC1−x phase was stabilized due to the small crystallite sizes. In addition, a thin layer of amorphous carbon was present on the powder surface due to the catalytic methane decomposition on the WC surface. The amount of oxidic and metallic residues in the product powder was minimized with the parameter optimization and the powder yield was increased up to about 50%. With further optimization of the process parameters and usage of improved flow breakers, the purity and yield of the product powder can be further improved. Since an application in the hardmetal section is not realistic at the moment, applications in the catalysis sector could be considered due to the small grain size and good catalytic activity of the cubic WC1−x phase.

Growth, crystal structure and temperature dependence of the band gap of Cu-=SUB=-2-=/SUB=-ZnGeS-=SUB=-4-=/SUB=- single crystals

Cu2ZnGeS4 single crystals were grown by chemical vapor transport reaction method. Their composition and crystal structure were determined. It was shown that the obtained single crystals crystallize in a tetragonal structure. The band gap of the obtained single crystals was determined basing on transmission spectrum in the region of the absorption edge in temperature range of 10-320 K. It was found that band gap width increases with decreasing of temperature. Keywords: Bridgman method, single crystals, crystal structure, transmission spectrum, band gap.

Single crystals of SnTe3O8 in the millimetre range grown by chemical vapor transport reactions.

Tin(IV) trioxidotellurate(IV), SnTe3O8, is a member of the isotypic M IVTeIV 3O8 (M = Ti, Zr, Hf, Sn) series crystallizing with eight formula units per unit cell in space group Ia . In comparison with the previous crystal structure model of SnTe3O8 based on powder X-ray diffraction data [Meunier & Galy (1971 ▸). Acta Cryst. B27, 602-608], the current model based on single-crystal X-ray data is improved in terms of precision and accuracy. Nearly regular [SnO6] octa-hedra (Sn site symmetry ..) are situated in the voids of an oxidotellurate(IV) framework built up by corner-sharing [TeO4] bis-phenoids (Te site symmetry 2..). A qu-anti-tative structural comparison revealed a very high degree of similarity for the structures with M = Ti, Zr, Sn in the M IVTe3O8 series.

From amorphous red phosphorus to black phosphorus crystal: An optimization, controllable and highest yield synthesis process

Understanding the growth mechanism of large crystals and high-quality of black phosphorus (BP) is a fundamental challenge to further study its physical properties. The BP was prepared from amorphous red phosphorus (RP), by short-way chemical vapor transport (CVT) reaction using the addition of small quantities of copper, tin, and tin(IV) iodide as reaction promoters. The method used in this present work is currently developed by our research laboratory for preparation of BP. In fact, a series of experiments was designed to understand and optimize the preparation conditions (the catalyst's choice (Cu), temperature, time, dimensions of quartz tube …) of this surprisingly easy and effective method and to ensure a high BP conversion ratio (wt%) from RP with high purity, high crystallinity, and large size of orthorhombic BP (flakes size ∼ 1 cm), It’s the main goal of this work. The products recovered in the hot and cold zones of the tube are analyzed by X-ray diffraction (XRD) to give an idea of the role of mineralizers (Cu,Sn, and SnI4) allowing the synthesis of BP. Decomposition of reaction system (RP/Cu/Sn) with the tin(IV) iodide should lead to the formation of the condensed phases represented by Cu4SnP10,Sn4P3, CuSn,Cu2P7, SnI4 and P2O5could be detected at a hot zone of the tube. The characterizations of the prepared BP were carried out also using Raman spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy.

A Study of the Possibility of Obtaining Deposited Coatings based on Intermetallic Titanium and Aluminum Compounds using the Chemical Vapor Transport Method

Theoretical and experimental investigations of processes of titanium-aluminum coating formation on refractory wire substrates by the Chemical Vapor Transport Reactions (CVT) method were carried out. Modelling of CVT was based on the thermodynamic analysis of an equilibrium iodide system implying the presence of one of titanium aluminides in the condensed phase, titanium and aluminum iodides in the gas phase, as well as atomic and molecular iodine. The fact that the volatility and stability of various metals are strongly interrelated was considered as a working hypothesis, which made it possible to obtain a number of alloys with the simultaneous decomposition of metal iodides constituting an alloy. Experiments on the deposition of titanium-aluminum coatings were conducted in a quasi-closed reactor, which allowed us to obtain deposited coatings on long-length refractory substrates

Asymmetric misfit nanotubes: Chemical affinity outwits the entropy at high-temperature solid-state reactions

Asymmetric two-dimensional (2D) structures (often named Janus), like SeMoS and their nanotubes, have tremendous scope in material chemistry, nanophotonics, and nanoelectronics due to a lack of inversion symmetry and time-reversal symmetry. The synthesis of these structures is fundamentally difficult owing to the entropy-driven randomized distribution of chalcogens. Indeed, no Janus nanotubes were experimentally prepared, so far. Serendipitously, a family of asymmetric misfit layer superstructures (tubes and flakes), including LaX-TaX2 (where X = S/Se), were synthesized by high-temperature chemical vapor transport reaction in which the Se binds exclusively to the Ta atoms and La binds to S atoms rather than the anticipated random distribution. With increasing Se concentration, the LaS-TaX2 misfit structure gradually transformed into a new LaS-TaSe2-TaSe2 superstructure. No misfit structures were found for xSe = 1. These counterintuitive results shed light on the chemical selectivity and stability of misfit compounds and 2D alloys, in general. The lack of inversion symmetry in these asymmetric compounds induces very large local electrical dipoles. The loss of inversion and time-reversal symmetries in the chiral nanotubes offers intriguing physical observations and applications.

Light-matter interactions in high quality manganese-doped two-dimensional molybdenum diselenide

Introducing magnetic dopants into two-dimensional transition metal dichalcogenides has recently attracted considerable attention due to its promising applications in spintronics and valleytronics. Herein we realized manganese-doped molybdenum diselenide (MoSe2) single crystal via chemical vapor transport (CVT) reaction, containing up to 2.9% (atomic concentration) Mn dopants, and investigated the light-matter interaction in these samples. We observed a suppressed trion intensity, a longer photoluminescence lifetime, and prominent blue- and red-shift of E 2g 2 (in-plane) and A1g (out-of-plane) Raman modes, respectively. Moreover, the Mn dopants increase the valley Zeeman splitting of the MoSe2 monolayer by ∼50%, while preserving the linear dependence on magnetic field. First-principles calculations indicate that the spin-polarized deep level defect states are formed due to the Mn substitutional dopants in the MoSe2 lattice. The resulting defect potential favors the funnelling of excitons towards the defects. The Mn dopants reduce the magnitude of the interatomic force constants, explaining the red-shift of the A1g mode. The Mn atoms and their immediate Mo and Se neighbors carry significant magnetic moments, which enhance the observed exciton g-factors due to the exchange interactions affecting defect-bound excitons.

Controllable preparation of crystalline red phosphorus and its photocatalytic properties.

Single-element phosphorus has received extensive attention in recent years because of its remarkable photocatalytic properties. In the present experiment, amorphous red phosphorus was controllably transformed into [P12(4)]P2[and Hittorf's phosphorus structures by performing bismuth catalysis. The temperature-controllable chemical vapor transport reaction realized the conversion of more than 90% of amorphous red phosphorus to single-phase crystalline red phosphorus. Under very mild ultrasonic treatment, the high-quality [P12(4)]P2[microbelts and Hittorf's phosphorus microrods were stripped into a few layers of nanobelts and sheet-like structures, respectively. As non-metallic catalysts, their rapid photocatalytic degradations of pollutants (methyl orange) and high hydrogen evolution rates revealed the rapid charge transfer and application potential of the crystalline red phosphorus catalyst. The results of this work could provide new ideas for the development of phosphorus-based crystalline photocatalytic systems.

Elucidating the physical properties of the molybdenum oxide Mo4O11 and its tantalum substituted variant Mo2Ta2O11

Abstract Although γ/η-Mo4O11 and Mo2Ta2O11 are used in a variety of industrial applications and can easily be synthesized in a chemical vapour transport (CVT) process or reactions in silica ampoules, respectively, only few data are available concerning their physical properties. In this paper, we further explore the properties of the three compounds with respect to their thermal and magnetic behavior, surface composition, and Raman spectroscopic properties.

Magnetic studies of monoclinic Cu4O(SeO3)3, a copper-oxo-selenite derivative

Cu4O(SeO3)3 is a copper-oxo-selenite belonging to the CuxO(SeO3)(x–1) family of the topological chiral magnet Cu2OSeO3. We report magnetometry and specific heat data measured in a monoclinic Cu4O(SeO3)3 single crystal grown through a Chemical Vapour Transport (CVT) reaction. Our study shows a typical antiferromagnetic behaviour, with a Néel temperature TN = 58 K, similar to that of the Cu2OSeO3 and an additional transition at 13 K. The effective magnetic moment per Cu atom is 1.84 μB, close to the expected theoretical value for Cu2+. The low-temperature M(H) curves, show a transition starting at Hc1 ~ 400 Oe at 1.8 K shifting to a lower value of ~ 280 Oe at 30 K, likely from a helical into a conical intermediate phase, and a second transition at Hc2 ~ 1 kOe, above which the net moment increases linearly with applied field. The magnetisation moment value in a 90 kOe field is 0.053 μB/Cu at 1.8 K and attains a maximum value of 0.061 μB at 13 K. Low-temperature specific heat measurements confirm the presence of the magnetic transition at 13 K, slightly shifting to lower temperatures under an applied magnetic field.