Vanadium Oxide Layers Research Articles

Synthesis, crystal structures and magnetic properties of organically templated new layered vanadates: [C4H8NH2]V3O7, [(CH3)2NH2]V3O7, [C5H10NH2]V3O7 and [C2H5NH3]V3O7

Four new layered mixed-valance vanadium oxides, which contain the interlamellar organic cations pyrolidinium, dimethylammonium, piperidinium, and ethylammonium, have been prepared under hydrothermal conditions and their structures determined. All four structures contain vanadium oxide layers constructed from V5+O4 tetrahedra and pairs of V4+O5 square pyramids with the protonated organic amines occupying the interlayer space. The materials are further characterized by thermal analysis, FTIR and scanning electron microscopy. Magnetic susceptibility studies of the first three compounds reveal a spin-gap behavior explained by an isolated antiferromagnetic dimers model. Large values of the exchange constants J = 325 − 480 K were found and the dependence of J upon the structural parameters was analyzed assuming a kinetic exchange mechanism.

Hydrothermal synthesis and crystal structure of a layered vanadium oxide with an interlayer metal coordination complex: [Co(phen) 3][V 10O 26]·H 2O

A novel compound, [Co(phen) 3][V 10O 26]·H 2O, was hydrothermally synthesized and characterized by single-crystal X-ray diffraction. This compound crystallizes in the orthorhombic space group Ccca with a=13.447(3), b=29.936(6), c=23.252(5) Å, V=9360(3) Å 3, Z=8 and R=0.0285. Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 1.36< θ<24.99°. The structure of the compound consists of vanadium oxide layers, which are built up from the infinite VO 4 chains by corners and edges sharing. The [Co(phen) 3] 2+ complexes occupy the interlayer space and contact each other via π− π stacking interactions of the phen groups to form infinite one-dimensional chains.

Redox Behavior of Vanadium Oxide Nanotubes As Studied by X-ray Photoelectron Spectroscopy and Soft X-ray Absorption Spectroscopy

Ex situ soft X-ray absorption spectroscopy (SXAS) and X-ray photoelectron spectroscopy (XPS) were used to study the redox behavior of sodium-containing vanadium oxide (Na−VOx) nanotubes in a rechargeable Li battery context. This nanotubular material consists of scroll-like layers of vanadium oxide separated by structure-directing agents, in this case Na+ ions. As lithium ions are inserted into the Na−VOx nanotubes, the V 2p peak weight shifts toward lower energies. This effect can be seen in both the SXAS and XPS results. Average oxidation states could be obtained from the XPS results, and these agree well with those estimated from electrochemical measurements. At potentials below 2.0 V, there is a coexistence of V(V), V(IV), and V(III), which suggests that some of the vanadium is inaccessible to reduction during the first cycles.

Structure of Vanadium Oxide (V2O3) Grown on Cu3Au(100)

The epitaxial growth of vanadium oxide (V2O3) has been investigated by scanning tunneling microscopy (STM), low energy ion back-scattering (ISS) and low energy electron diffraction (LEED). Direct evaporation of vanadium onto metal surfaces (Cu, Au or Cu3Au) gives rise to massive surface alloying. The attempt to oxidize the vanadium film by consequent oxygen exposure leads to the formation of rough VO x films of poor quality and mixed valency. A new way of oxide formation has been developed by preoxidation of a Cu3Au substrate, which acts positively in two ways since it prevents completely alloy formation and also forces strong surface wetting of the vanadium oxide. As a result, two-dimensional layer growth of good quality has been achieved. Depending on the preoxygen content at Cu3Au(100), the amount of V deposition and annealing temperature, different epitaxial layers of vanadium oxides can be prepared. In particular, the surface structure of V2O3(0001) was investigated. The surface structure appears completely different from the half layer metal termination at Cr2O3(0001). Specifically, the full vanadium layer stabilized by one third of an oxygen layer located in pseudo bridge positions close to regular oxygen positions of a next layer. Close to defects the full vanadium layer appears also without oxygen stabilization.

The Structure and Electrochemical Performance of Na + ­ , K + ­ , and Ca2 + -Vanadium Oxide Nanotubes

Vanadium oxide nanotubes, with embedded or -ions, were synthesized and investigated structurally and electrochemically in a Li-battery context. The nanotubes consist of scroll-like layers of vanadium oxide separated by structure-directing primary amines or metal cations. X-ray diffraction and Raman spectroscopy provided structural information of the sheets. It was found that the structure within the layers is similar to the double-layered Galvanostatic measurements showed that the materials cycle reversibly for >100 cycles, giving average capacities of around 150 mAh/g (1.8-3.5 V vs. © 2003 The Electrochemical Society. All rights reserved.

Solvothermal synthesis and characterization of a layered pyridinium vanadate, (C5H6N)V3O7

A new layered vanadium oxide, (C5H5NH)V3O7, has been synthesized by a solvothermal process at 200 °C; this is the first vanadium oxide to have an aromatic intercalate between the V3O7 sheets, and it has a monoclinic structure with space group P21 and lattice parameters a = 7.5296(6) A, b = 6.6592(8) A, c = 10.1513(12) A and β = 94.460(2)°.

Hydrothermal Synthesis and Characterization of (H3N(CH2)4NH3)[V6O14

A new layered vanadium oxide [H 3 N(CH 2 ) 4 NH 3 ](V 6 O 14 ) was synthesized hydrothermally under autogenous pressure at 180°C for 48 h from a mixture of H 2 N(CH 2 ) 4 NH 2 and V 2 O 5 in aqueous solution. Its structure was determined from single-crystal X-ray diffraction at room temperature with final R =0.0774 and R w =0.0893. It crystallizes in the monoclinic system (space group P 2 1 / n with a =9.74(2) Å, b =6.776(5) Å, c =12.60(2) Å, β =96.1(1)°, V =827(2) Å 3 and Z=2). This compound contains mixed-valence V 5+ /V 4+ vanadium oxide layers built from [V V O 4 ] tetrahedra and pairs of edge-sharing [V IV O 5 ] square pyramids with protonated organic amines occupying the interlayer space.

Hydrothermal Synthesis and Characterization of (H 3N(CH 2) 4NH 3)[V 6O 14

A new layered vanadium oxide [H 3N(CH 2) 4NH 3](V 6O 14) was synthesized hydrothermally under autogenous pressure at 180°C for 48 h from a mixture of H 2N(CH 2) 4NH 2 and V 2O 5 in aqueous solution. Its structure was determined from single-crystal X-ray diffraction at room temperature with final R=0.0774 and R w=0.0893. It crystallizes in the monoclinic system (space group P2 1/ n with a=9.74(2) Å, b=6.776(5) Å, c=12.60(2) Å, β=96.1(1)°, V=827(2) Å 3 and Z=2). This compound contains mixed-valence V 5+/V 4+ vanadium oxide layers built from [V VO 4] tetrahedra and pairs of edge-sharing [V IVO 5] square pyramids with protonated organic amines occupying the interlayer space.

Composition and structure of ultrathin vanadium oxide layers deposited on SnO 2( [formula omitted

Ultrathin layers of vanadium oxides on SnO 2(1 1 0) were prepared by evaporation of metallic vanadium in oxygen atmosphere (partial pressure of O 2: 1×10 −5 Pa) at room temperature (RT). Vanadium oxide layers were deposited on the (4×1) reconstructed surface of SnO 2(1 1 0). The substrate surface was prepared by cycles of sputtering and annealing in vacuum. X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering (LEIS) results show that the growth mechanism of the oxide layers involves the migration of tin atoms from the substrate onto the surface of the film already at RT. Although no LEED pattern is observed, the X-ray photoelectron diffraction (XPD) measurements reveal that the vanadium oxide films grow epitaxially on the substrate surface. The similarity between the Sn 3d XPD pattern measured for the clean SnO 2(1 1 0) surface and the V 2p pattern measured for the oxide layers suggests that these films have a structure close to that of the substrate (rutile-type lattice). The present results can be explained with a formation of a vanadium oxide of the series V n O 2 n−1 with 4⩽ n⩽8. These so called Magnéli phases of vanadium oxides have structures similar to that of rutile VO 2. This interpretation was confirmed by comparison of multiple scattering calculations with the experimental XPD curves. The vanadium oxide films are stable and the formation of mixed vanadium–tin oxide does not occur after annealing in vacuum at ≈800 K. The XPD data seem to indicate that tin atoms are present at the surface as a two-dimensional phase. STM images collected for the annealed phases reveal a morphology consistent with the XPS and LEIS results.

The zinc–vanadium–oxygen–water system: hydrothermal synthesis and characterization

Abstract Zinc forms a variety of structures with vanadium oxide. We review and report here on four compounds formed by mild hydrothermal synthesis in the presence of the tetramethyl ammonium ion, which tends to stabilize layered vanadium oxide structures. These invariably contain protons either in the form of hydroxyl ions or as structural water. The compounds include Zn 3 (OH) 2 (V 2 O 7 )•2H 2 O, which contains V 2 O 7 pillars, Zn 2 (OH) 3 (VO 3 ), and the two related double sheet vanadium oxides δ -Zn 0.8 V 4 O 10 •0.6H 2 O and [N(CH 3 ) 4 ] 4 [Zn 4 V 21 O 58 ]. We report the new structure of the last, which was determined from micron size crystals, and compare it to other double sheet structures. These compounds provide model systems to study ionic mobility and reversible redox chemistry.

A highly reduced polyoxoanion with phosphorus-centered alternate layers of Mo/V oxides, [PMo 2VMo 6VIV 4IVO 40(V IVO) 2] 9−

An unusual polyoxometalate [H 2N(C 2H 4) 2NH 2] 4(H 3O)[PMo 2 VMo 6 VIV 4 IVO 40(V IVO) 2]·H 2O is hydrothermally synthesized and characterized by IR, UV–VIS, elemental analyses, X-ray photoelectron spectrum, ESR, TG and Single crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Pbca with a=15.227(5), b=19.491(4), c=18.737(3) Å, V=5123(2) Å 3, Z=4, and R 1( wR 2)=0.0726(0.1416). The compound contains an unusual highly reduced pseudo-Keggin type polyoxoanion and exhibits an interesting phosphorus-centered alternate arrangement of layers of molybdenum and vanadium oxides.

Hydrothermal synthesis, structure and characterization of a novel layered vanadium oxide with metal coordination complexes: [Ni(en)2][V6O14

The hydrothermal reaction of V2O5, Ni(NO3)2·6H2O, ethylenediamine and H2O in the molar ratio of 1∶1∶3.5∶519 at 180 °C yields black plates of [Ni(en)2][V6O14]. This compound has been characterized structurally, magnetically, electrically, and spectroscopically. The crystal structure consists of novel mixed-valence vanadium oxide layers and interlayer metal coordination complexes. Each of the three VO5 square pyramids share two edges to form a V3O11 group. The V3O11 groups are connected through sharing edges to produce a linear ribbon. Adjacent strips share corners to form a layer structure. The two oxygen atoms from the neighbouring vanadium oxide layers are coordinated to each nickel atom in a trans-fashion, and form a three-dimensional framework structure. An EHT (Extended Huckel Theory) calculation was performed to analyze the electronic structure, and the electrical resistivity measurements confirmed the expected semiconducting behavior of [Ni(en)2][V6O14].

Stable Pd / V 2 O 5 Optical H 2 Sensor

Thin films of Pd exhibit a change in their optical properties when exposed to hydrogen. A new sensor structure consisting of a combined Pd and thin film stack has been developed for optical detection of hydrogen. Unlike a singular palladium thin film sensor, the new structure is durable and allows detection of hydrogen concentration in excess of 4%. The sensor exhibits a very fast response time and can be cycled for over 500 cycles without degradation of performance. It has been found that the stoichiometry of oxygen in the vanadium oxide layer is very critical for its reaction with hydrogen and greatly affects the overall sensor stability. A study of the operating mechanism reveals that the formation of palladium hydride is singularly responsible for the optical modulation while the vanadium oxide layer offers no contribution (after the initial irreversible color change from yellow to blue). Subsequent reversible hydrogen insertion into vanadium oxide does take place as evidenced by the Raman data even though no optical change in the visible spectrum is observed. © 2002 The Electrochemical Society. All rights reserved.

Hydrothermal syntheses and crystal structures of two-dimensional (2D) layered vanadium oxide complexes: M(bipy)(H2O)V2O6 (M = Ni, Co, bipy = bipyridine) and [Ni(bipy)2V6O17

Double layered vanadium oxide metal coordination complexes, [Ni(bipy)(H2O)V2O6]∞1 and {[Ni(bipy)2]2V6O17}∞2, have been isolated from the same hydrothermal reaction container. X-Ray crystallography shows that 1 consists of unique two-dimensional layers constructed from a vanadium oxide chain {V2O6}2n−n and covalently linked by Ni(bipy)(H2O)2+ subunits. In contrast 2 and the previously reported Zn(bipy)2V6O17 are isomorphic compounds. Only [Co(bipy)(H2O)V2O6]∞, 3, was obtained when cobalt was substituted for nickel in a similar reaction, and X-ray diffraction analysis reveals that the topology of 3 is essentially identical to that of 1. The magnetic behavior of 1 and 2 suggests a dominant single ion effect with only very weak magnetic interactions.

Synthesis of Novel Vanadium Oxide Nanotubes and Nanofibers

ABSTRACTWe are exploring the synthesis and properties of structured vanadium oxides mainly nanotubes and nanorods. Nanotubes initially formed with surfactant templates have been readily exchanged with simple cations without change of the basal-plane structure. These compounds contain d-like vanadium oxide layers with the vanadium in VO6 octahedra. This structure is particularly suitable for redox reactions. In this paper we report on synthesis of vanadium oxide, (NH4)xV2O5-d·nH2O rods using organic polymer as template. This compound has been synthesized by sol-gel reaction and subsequent hydrothermal treatment. TGA, SEM, XRD and FTIR were used to characterize this compound. Thermal analysis of this compound shows that the fibrous morphology is maintained when it is heated in nitrogen and oxygen above 300 °C. However, in both cases the size of the fibers decreases. Performance of this compound as cathode material in secondary electrolyte has been investigated using LiPF6 as electrolyte. A capacity of 140 mAh/g was obtained which remained fairly constant with up to at least 10 cycles. We also investigated electrochemical behavior of thermal products.

Lithium insertion/deinsertion properties of new layered vanadium oxides obtained by oxidation of the precursor H 2V 3O 8

The electrochemical behavior of the three new vanadium oxides M y H 1− y V 3 VO 8 (M=Li, Na, K; y=0.6–0.9) towards lithium insertion was studied. For each compound, the main insertion phenomena, and the lithium amount which can be inserted, were determined from galvanostatic studies performed at different rates. In order to better explain the differences between the compounds, the galvanostatic intermittent titration technique was used and chronoamperometry experiments were performed. Cyclability studies have shown that the performances of M 0.6H 0.4V 3O 8 (M=Li, K) are not better than those of H 2V 3O 8. On the contrary, Na 0.9H 0.1V 3O 8 presents very interesting lithium insertion properties, with a specific capacity of 215 mAh g −1 in the 1.5–4 V voltage range at C/10, and a capacity loss at the 40th cycle remaining smaller than 2.5%. Na 0.9H 0.1V 3O 8 is therefore a good candidate as positive electrode material for rechargeable lithium batteries.

Synthesis of Polyoxovanadates from Aqueous Solutions

Polyoxovanadates have been synthesized from aqueous solutions of VV in the presence of inorganic Na+ and organic [N(CH3)4]+ cations. Decavanadate crystals are precipitated at room temperature around pH 7, whereas layered compounds Na[V3O8].H2O and N(CH3)4[V4O10] are formed at the same pH under hydrothermal conditions. In situ51V NMR experiments show that upon heating solute decavanadate species are progressively transformed into cyclic metavanadates [V4O12]4−. A chemical mechanism is suggested for the formation of these layered vanadium oxides. It involves the ring-opening polymerization of cyclic metavanadates arising from co-ordination expansion favored by protonation or vanadium reduction.

The First Vanadium Oxide Nanotubes Containing an Aromatic Amine as Template

A new vanadate has been prepared in high yield by reacting vanadium(V) triisopropoxide and 3-phenylpropylamine in solution, followed by hydrolysis and hydrothermal treatment of the intermediate product. For the first time, an aromatic amine has successfully been applied as structure-directing template for the synthesis of vanadium oxide nanotubes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate the tubular morphology of the phenylpropylamine vanadium oxide nanotubes obtained. The size and structure are similar to that of vanadium oxide nanotubes formed with aliphatic amines. The tube walls comprise layers of vanadium oxide with the organic template intercalated in between. The interlayer distance is ca. 2.1 nm, and the structure of the VOx layers can be described by a square lattice with a≈0.61 nm. Furthermore, the TEM investigation has revealed the presence of many defects in the wall structure.

The First Vanadium Oxide Nanotubes Containing an Aromatic Amine as Template

A new vanadate has been prepared in high yield by reacting vanadium(V) triisopropoxide and 3-phenylpropylamine in solution, followed by hydrolysis and hydrothermal treatment of the intermediate product. For the first time, an aromatic amine has successfully been applied as structure-directing template for the synthesis of vanadium oxide nanotubes. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrate the tubular morphology of the phenylpropylamine vanadium oxide nanotubes obtained. The size and structure are similar to that of vanadium oxide nanotubes formed with aliphatic amines. The tube walls comprise layers of vanadium oxide with the organic template intercalated in between. The interlayer distance is ca. 2.1 nm, and the structure of the VOx layers can be described by a square lattice with a≈0.61 nm. Furthermore, the TEM investigation has revealed the presence of many defects in the wall structure.

Manganese Vanadium Oxide Nanotubes: Synthesis, Characterization, and Electrochemistry

Vanadium oxide nanotubes have been formed from the layered vanadium oxide precursor V2O5+δ[C12H25NH3]. Both the precursor and tubes have been characterized. The black nanotubes have a relatively low thermal stability in oxygen, being oxidized to V2O5 below 200 °C. A new manganese vanadium oxide nanotube, Mn0.1VO2.5+δ·nH2O, has been synthesized by ion exchange. These manganese tubes have a tetragonal layer with a = 6.157 (3) Å and an interlayer spacing c = 10.52 (3) Å. The nanotubes react with lithium chemically and are also electrochemically active in lithium cells. Two lithium atoms per vanadium can be incorporated chemically from n-butyllithium into both the manganese and the alkylammonium nanotubes. The manganese compound electrochemically intercalates 0.5 lithium per vanadium to a 2 V cutoff, giving a capacity of 140 A h/kg.