Vapor Transport Reaction Research Articles

Synthesis and magnetic studies of nanocrystalline Cu2OSeO3, a chiral topological magnet

Abstract Topological spin textures, such as magnetic skyrmions observed in certain chiral magnets, are one of the most interesting ordered phases in condensed matter. A skyrmion is a swirling spin structure carrying a topological quantum number. Skyrmions were first observed in MnSi, in 2009, and later observed in Cu 2 OSeO 3 , a chiral antiferromagnet with T N = 58 K that can be synthesized by reacting CuO and SeO2 at 600 ° C . Using a transport agent (typically ammonium chloride) in a chemical vapour transport reaction, single crystals can be grown. As skyrmion lattices may find use in nanotechnological devices, such as data storage systems and in other applications, the magnetic properties of nano-sized compounds deserve to be investigated. The following work presents the synthesis and magnetic studies of the nanocrystalline form of Cu 2 OSeO 3 obtained by an alternative route, thermal decomposition of CuSeO3·2 H2O. This procedure afforded nanostructured samples of reasonable purity ( > 95 % ) . Structural, morphological and magnetic characterization of these samples are reported, aiming to study the effect of nanostructuring on the magnetic phases, in particular the presence and stability of the skyrmionic lattice.

Crystal Chemistry, Optical Spectroscopy and Crystal Field Calculations of Co3TeO6 and Solid Solutions Co3–xZnxTeO6

Solid solutions Co3–xZnxTeO6 (x = 0–3) were prepared both in polycrystalline and single‐crystalline form using solid state reactions and chemical vapour transport reactions, respectively. Miscibility between the isotypic end members was established over the complete range (C2/c, Z = 12, a ≈ 14.85, b ≈ 8.83, c ≈ 10.34 Å, β ≈ 93°). Crystal structure determinations, performed on basis of single crystal laboratory X‐ray (at 295 K) and synchrotron (at 10 and 100 K) data of Co3TeO6 and selected solid solutions, revealed no structural phase transition and allowed a detailed insight into the Co → Zn substitution mechanism. The coordination polyhedra of the five crystallographically independent M2+ cations are distorted octahedra (for three cations), one distorted tetrahedron and one distorted square pyramid. With increasing Zn content the polyhedral distortions increase, and the preference of the Zn2+ cation for the tetrahedral coordination becomes distinctive. Optical absorption and diffuse reflectance spectroscopy reveal extraordinary strong crystal field absorption effects, over wide x ranges predominantly governed by Co2+ in the single tetrahedral and one strongly acentric distorted octahedral site. Superposition Model crystal field calculations yield intrinsic and power‐law exponent parameters in general agreement with previous data for Co2+. The five cation sites show comparatively high crystal field strengths at generally very low interelectronic repulsion parameters, indicating prominent covalent contribution to Co–O bonding in Co3–xZnxTeO6 solid solutions.

Uniform Tellurium Doping in Black Phosphorus Single Crystals by Chemical Vapor Transport.

Doping has been a reliable way to improve the properties of black phosphorus (BP). However, a uniform and large amount of doping in BP remains a challenge. Herein, the synthesis of tellurium-doped black phosphorus (Te-doped BP) single crystals with high crystalline quality is achieved by the chemical vapor transport reaction method. The synthetic route enables a uniform and relatively large amount (up to 0.5% atomic ratio) of Te-doping in BP single crystals. The electrocatalytic oxygen evolution reaction (OER) properties of few-layer Te-doped BP nanosheets prepared by liquid exfoliation were also investigated for the first time. Electrochemical tests demonstrated that the OER onset-potential of undoped and Te-doped BP nanosheets was 1.63 and 1.49 V, respectively. The result implies that doping provides an effective route to enhance the electrochemical OER performance of BP.

Chemical Pressure Stabilization of the Cubic B20 Structure in Skyrmion Hosting Fe1–xCoxGe Alloys

Iron monogermanide (FeGe) with the noncentrosymmetric cubic B20 structure is a well-known helimagnet and a magnetic skyrmion host with a relatively high ordering temperature (∼280 K). FeGe and related metal monogermanide compounds, such as CoGe and MnGe, have several structural polymorphs and typically require high pressure (∼4 GPa) and high temperature (∼1000 °C) to synthesize in the cubic B20 structure. Here, we report that the cubic B20 phase of both FeGe and alloys of Fe1–xCoxGe could in fact be formed without the application of high pressure by simply reacting elemental powders at modest temperatures (550 °C). Furthermore, the incorporation of Co into Fe1–xCoxGe (0.05 ≤ x ≤ 0.1) stabilizes the cubic B20 structure up to 650 °C, which we propose is caused by chemical pressure induced by the incorporation of Co into the lattice. Interestingly, chemical vapor transport reactions using the Fe1–xCoxGe alloys as precursors yield plentiful growth of large (0.1 to 1 mm) single crystals of pure FeGe. Magnetic ...

Facile Syntheses of pure Uranium(III) Halides: UF3, UCl3, UBr3, and UI3

Herein we describe a convenient lab scale synthesis for pure and solvent‐free binary uranium(III) halides UCl3, UBr3, and UI3. This is achieved by the reduction of the respective uranium(IV) halides with elemental silicon in borosilicate ampoules at moderate temperature. The silicon tetrahalides SiX4 formed as a side product are utilized for the removal of excess starting material via a chemical vapor transport reaction. The syntheses introduced herein avoid the need for pure metallic uranium and are based on uranium(IV) halides synthesized from UO2 and the respective aluminum halides and purified by chemical vapor transport. These uranium(III) halides are obtained in single crystalline form. A similar reaction yields UF3 as a microcrystalline powder. However, no beneficial transport reaction occurs with this halide. Also, a higher temperature has to be applied and steel ampoules have to be used. The identities and purity of the products were checked by powder X‐ray diffraction as well as IR spectroscopy. The synthesis of UI3 enabled its crystal structure determination on single crystals for the first time. UI3 crystallizes in the PuBr3 structure type with space group type Cmcm and a = 4.3208(9), b = 13.923(3), c = 9.923(2) Å, V = 596.9(2) Å3, and Z = 4 at T = 100 K.

Mechanical exfoliation and electrical characterization of a one-dimensional Nb2Se9 atomic crystal

A novel semiconductor 1D nanomaterial, Nb2Se9, was synthesized on a bulk scale via simple vapor transport reaction between niobium and selenium. Needle-like single crystal Nb2Se9 contains numerous single Nb2Se9 chains linked by van der Waals interactions, and we confirmed that a bundle of chains can be easily separated by mechanical cleavage. The exfoliated Nb2Se9 flakes exhibit a quasi-two-dimensional layered structure, and the number of layers can be controlled using the repeated-peeling method. The work function varied depending on the thickness of the Nb2Se9 flakes as determined by scanning Kelvin probe microscopy. Moreover, we first implemented a field effect transistor (FET) based on nanoscale Nb2Se9 flakes and verified that it has p-type semiconductor characteristics. This novel 1D material can form a new family of 2D materials and is expected to play important roles in future nano-electronic devices.

Oxocentered Units in Three Novel Rb‐Containing Copper Compounds Prepared by CVT Reaction Method

Three novel copper compounds, Rb4Cu4OCl10 (I), Rb[Cu3O](SeO3)2Cl (II), and RbCu3(OH)(SeO3)Cl4(H2O)3 (III) were prepared by chemical vapor transport (CVT) reactions method from mixtures of CuO, SeO2, RbCl, and CuCl2. The crystal structures of the three compounds were determined by direct methods. Compound I is a Rb analogue of ponomarevite, K4Cu4OCl10. Its crystal structure contains {[OCu4]Cl10}4– clusters with oxocentered [OCu4]6+ tetrahedra as cores. The clusters are linked by the Rb+ cations. The crystal structure of II contains complex {[O2Cu6](SeO3)4Cl2}2– layers formed by dimers of edge‐sharing [OCu4]6+ tetrahedra interlinked via selenite groups and Cl– anions. The crystal structure of III is based upon {[(OH)Cu3](SeO3)}3+ layers formed by the [(OH)Cu3]5+ tetrahedra attached to (SeO3)2– groups. The layers are linked via Cl– anions and via hydrogen bonds to H2O molecules.

Synthesis and crystal structure of Fe[(Te1.5Se0.5)O5]Cl, the first iron compound with selenate(IV) and tellurate(IV) groups

During the search for selenium analogues of FeTe2O5Cl, the new iron (III) tellurate(IV) selenate(IV) chloride with the composition Fe[(Te1.5Se0.5)O5]Cl was synthesized by chemical vapor transport (CVT) reaction and characterized by TGA-, EDX-,SCXRD-analysis, as well as IR and Raman spectroscopy. It was found that Fe[(Te1.5Se0.5)O5]Cl crystallizes in the monoclinic space group P21/c with unitcell parameters a = 5.183(3) Å, b = 15.521(9) Å, c = 7.128(5) Å and β = 107.16(1)°. The crystal structure of Fe[(Te1.5Se0.5)O5]Cl represents a new structure type and contains electroneutral heteropolyhedral layers formed by dimers of the [FeO5Cl]8– octahedra, linked via common O-O edges, and mixed [Te3SeO10]4- tetramers. Adjacent layers are stacked along the b axis and linked by weak residual bonds. The new compound is stable up to 420 °C. DFT calculations predict Fe[(Te1.5Se0.5)O5]Cl to be a wide-gap semiconductor with the band gap of ca. 2.7 eV.

Chemical Vapor Transport Reactions – Arguments for Choosing a Suitable Transport Agent

A variety of processes of crystal growth proceeds via the gas phase. If the initial solid material is volatilized in a heterogeneous reaction under presence of a gaseous reactant, the transport agent, the term Chemical Vapor Transport Reaction (CVT) is applied. Crystallization processes by CVT are known for both elements, intermetallics, binary and complex oxides, halides, chalcogenides, and pnictides. Even if the formation of volatile halides is a common feature of almost all vapor transport reactions, significant differences are there concerning the choice of a suitable transport agent depending on the nature of the initial solid phase. Actually, the appropriateness of transport agents for the respective transport reaction can be described in a thermodynamic way. Besides some basic principles for systematic evaluation more practical recommendations for suitable experimental conditions are given for CVT of different classes of inorganic materials.

Preparation and investigation of GaxGe25As15Se60-x (x = 1 ÷ 5) glasses

Chalcogenide glasses of GaxGe25As15Se60-x (x = 0; 1; 2; 3; 4; 5) compositions are prepared; their transmission range, optical band gap energy, thermal properties and stability against crystallization are studied. It is shown that these glasses have a high transparency in the mid-IR region (from 0.8 to 15 μm), a high glass transition temperature (≥320 °C) and a low tendency to crystallize. The optical band gap energy of GaxGe25As15Se60-x (x = 0; 1; 2; 3; 4; 5) glasses decreases from 1.68 to 1.43 eV as the gallium content increases and the selenium decreases. Their glass network, according to IR spectroscopy data, consists of Ge(Se1/2)4 tetrahedrons and AsSe3/2 pyramids. The Ga2Ge25As15Se58 and Ga3Ge25As15Se57 glasses have highest stability against crystallization. The content of hydrogen and oxygen impurities in the purest glass samples, fabricated using a combination of chemical distillation purification method and vapor transport reaction technique, does not exceed 0.06 ppm (wt) and 0.5 ppm (wt), respectively.

Hittorf's phosphorus: the missing link during transformation of red phosphorus to black phosphorus

Although orthorhombic black phosphorus (BP) single crystals have been successfully synthesized through a chemical vapor transport (CVT) reaction based on a red phosphorus/tin/iodine (RP/Sn/I2) system, the underlying nucleation and growth mechanism is poorly understood during the transformation of RP to BP. Particularly, little is known about the critical state of BP nucleation during the CVT process. Herein, we reveal that the BP nucleation and growth proceed from the crystalline monoclinic violet or Hittorf's phosphorus (HP), which is accurately confirmed via a series of structural and optical experimental identification approaches and supported by quantum chemical studies. We thus propose a step-by-step phase-induced nucleation and growth mechanism for the growth of BP single crystals by using a CVT reaction in a RP/Sn/I2 system. A better understanding of the transformation of RP to BP may pave the way for direct synthesis of phosphorene via a CVT method in the near future.

Crystal growth and crystal structures of six novel phases in the Mn/As/O/Cl(Br) system, as well as magnetic properties of α-Mn3(AsO4)2

Chemical vapour transport reactions (900°C → 820°C, Cl2 or Br2 as transport agent) of in situ formed Mn3(AsO4)2 yielded the orthoarsenates(V) α-Mn3(AsO4)2 and β-Mn3(AsO4)2 as well as the oxoarsenate(V) halide compounds Mn7(AsO4)4Cl2, Mn11(AsO4)7Cl, Mn11(AsO4)7Br and Mn5(AsO4)3Cl. The crystal structures of all six phases were determined from single crystal X-ray diffraction data. The crystal structures of α-and β-Mn3(AsO4)2 are isotypic with the corresponding phosphate phases γ- and α-Mn3(PO4)2, respectively, and are reported here for the first time. A comparative discussion with other structures of general composition M3(AsO4)2 (М = Mg; divalent first-row transition metal) is given. The unique crystal structures of Mn7(AsO4)4Cl2 and that of the two isotypic Mn11(AsO4)7X (X = Cl, Br) structures are composed of two [MnO5] polyhedra, two [MnO4Cl2] polyhedra (one with site symmetry 1¯), two AsO4 tetrahedra, and one [MnO5] polyhedron, three [MnO6] octahedra (one with site symmetry.m.), one [MnO4X], one [MnO5X] polyhedron and four AsO4 tetrahedra, respectively. The various polyhedra of the three arsenate(V) halides are condensed into three-dimensional framework structures by corner- and edge-sharing. Mn5(AsO4)3Cl adopts the chloroapatite structure. The magnetic and thermal properties of pure polycrystalline samples of a-Mn3(AsO4)2 were investigated in more detail. The magnetic susceptibility proves all Mn atoms to be in the oxidation state +2 yielding an effective magnetic moment per Mn atom of 5.9μB. Long-range antiferromagnetic ordering is observed below 8.2K consistent with the negative Curie-Weiss temperature of −50K derived from the high temperature susceptibility data.

ChemInform Abstract: Copper Polytellurite‐Chlorides with A2+ Cations (A: Cd, Pb) Obtained by CVT Reactions.

AbstractSingle crystals of Pb5Cu2(Te4O11)Cl8 (I) and CdCu2(Te3O8)Cl2 (II) are obtained by chemical vapor transport reactions of either a 3:1:1 mixture of CuCl2, TeO2, and PbO or a 1:2:1 mixture of CuCl2, TeO2, and CdO (evacuated quartz tube, 450→430 °C, 24 h).

Copper polytellurite-chlorides with A2 + cations (A[dbnd]Cd, Pb) obtained by CVT reactions

Two novel polytellurite-chlorides Pb5Cu2(Te4O11)Cl8 (1) and CdCu2(Te3O8)Cl2 (2) were obtained by a chemical vapor transport (CVT-reactions) reactions. The structure of 1 is based on [Pb5Cu2(Te4O11)]8+ one-dimensional blocks with full and partially occupied Cl sites around. The structure of 2 can be described as being formed by two types of one-dimensional units formed by Cd,Cu-centered polyhedra and TeO3, TeO4 pyramids sharing via common O atoms into electroneutral [CdCu2(Te3O8)Cl2]0 sheets. Obtaining of novel polytellurite-chlorides demonstrates effectiveness of CVT techniques for preparation of different tellurite-based complex layered materials.

Two-step heating synthesis of sub-3 millimeter-sized orthorhombic black phosphorus single crystal by chemical vapor transport reaction method

A facile and green strategy to synthesize orthorhombic black phosphorus ( o -BP) single crystals with high yield (~90%) and large size (sub-3 millimeter) is presented. The strategy was based on a two-step heating chemical vapor transport (CVT) reaction method, in which tin and iodine (Sn/I2) was used as mineralization additives and red phosphorus as precursor. Tin phosphide was the only by-product captured at the end of reaction, which greatly simplified the subsequent separation and purification processes of o -BP single crystals. The full width at half maximum (FWHM) of X-ray rocking curve of the as-grown o -BP was 21.65 arc sec, indicating its respectable crystalline quality. A bottom electrode structure field-effect transistor (FET) based on the multilayer phosphorene mechanically exfoliated from the as-grown o -BP single crystal was successfully fabricated through an all-dry transfer technique. Impressively, the FET based on a 6 nm thick multilayer (approximate 12 layers) phosphorene exhibited a record high hole mobility ( μ p) of 1744 cm2 V-1 s-1 and an admirable on/off current switching ratio ( I on/ I off) of ~104, which further proved the high-quality of the o -BP single crystals synthesized by the twostep heating CVT reaction method using the simple Sn/I2/red phosphorus system.

ChemInform Abstract: Flexible Ultraviolet—Visible Photodetector Based on HfS3 Nanobelt Film.

AbstractThe title nanobelts are synthesized by chemical vapor transport reaction of Hf and S powders (quartz tube, 650 °C, temperature gradient about 10 K/cm, 5 h).

Pathways for synthesis of new selenium-containing oxo-compounds: Chemical vapor transport reactions, hydrothermal techniques and evaporation method

Due to the low and close melting and sublimation temperatures (340 and 350°C, respectively), the crystal growth of selenates and/or selenites is generally achieved using either chemical vapor transport routes, hydrothermal methods due to the good solubility and reactivity of (SeO3)2− anions or isothermal evaporation synthesis. Here we report examples many new crystal structures obtained using these synthesis routes. Particularly, description of each process is given with theoretical and practical information assorted with description of selected structures.

On the band gap of Cu2ZnSn(S x Se1–x )4 alloys

The transmittance spectra of single-crystal Cu2ZnSnS4 and Cu2ZnSnSe4 compounds and Cu2ZnSn(SxSe1–x)4 alloys grown by chemical vapor-transport reactions are studied in the region of the fundamental absorption edge. From the experimental spectra, the band gap of the compounds and their alloys is determined. The dependences of the band gap on the composition parameter x of the alloy are constructed. It is established that the band gap nonlinearly varies with x and can be described as a quadratic dependence.

NaCl][Cu(HSeO3)2], NaCl-intercalated Cu(HSeO3)2: synthesis, crystal structure and comparison with related compounds

Abstract Single crystals of [NaCl][Cu(HSeO3)2] have been prepared by the chemical vapor transport reactions. Its crystal structure (monoclinic, C2/c, a = 13.9874(7), b = 7.2594(4), c = 9.0421(5) Å, β = 127.046(2)°, V = 732.81(7) Å3) is based upon electroneutral [Cu(HSeO3)2] sheets formed by corner sharing between the [CuO4] squares and (HSeO3) groups that are parallel to the (100) plane. Each (SeO2OH)– group forms the Oh1...O2 hydrogen bond to an adjacent hydroselenite group to constitute a [(SeO2OH)2]2– dimer that provides additional stabilization of the copper diselenite sheet. The [Cu(HSeO3)2] sheets alternate with the sheets consisting of zigzag–Na–Cl–Na–Cl–chains formed by Cl atoms and disordered Na sites. The chains are parallel to the c axis. The linkage between the alternating electroneutral [Cu(HSeO3)2] and [NaCl] sheets is provided by the Cu–Cl and Na–O bonds. The coordination of Na is fivefold and consists of three O and two Cl atoms. [NaCl][Cu(HSeO3)2] is a new member of the group of compounds based upon the M(HSeO3)2 layers (M2+ = Cu, Co, Cd). The prototype structure for this group is [Cu(HSeO3)2] that does not have any chemical species separating the copper hydroselenite layers. In other compounds, the interlayer space between the [Cu(HSeO3)2]0 layers is occupied by structural units of different complexity. [NaCl][Cu(HSeO3)2] can be considered as [Cu(HSeO3)2] intercalated with the NaCl layers consisting of one-dimensional–Na–Cl–Na–Cl–chains.

ChemInform Abstract: Coupling of Crystal Structure and Magnetism in the Layered, Ferromagnetic Insulator CrI3.

AbstractSingle crystals of CrI3 are grown by chemical vapor transport reaction of stoichiometric amounts of Cr and I2 in a temperature gradient (evacuated quartz tubes, 650 °C→500‐550 °C, several days).