Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Mechanochemical reactions between Ag2O and V2O5 to form crystalline silver vanadates

Solid-state reactions between Ag₂O and V₂O₅ were studied under ball-milling conditions. Single-phase crystalline Ag₄V₂O₇ was formed from the mixture of Ag₂O and V₂O₅ of corresponding (2:1) composition. The main component in the product when the Ag₂O mole fraction is less than V₂O₅ is amorphous AgVO₃, which is crystallized into needle-like α-AgVO₃ in the presence of water. Excess V₂O₅ was hydrated into V₂O₅·nH₂O intercalated with Ag⁺ ions. The mixtures with more than two parts of Ag₂O relative to V₂O₅ are composite materials of Ag₄V₂O₇ and Ag₃VO₄, together with Ag₂O. The crystalline phases in these systems resist attack by water.     

Phase stability and ionic conductivity in substituted La2W2O9

Different substitutions, i.e. Sr²⁺, Ba²⁺, K⁺, Nb⁵⁺ and V⁵⁺, have been performed in the triclinic α-La₂W₂O₉ structure in order to stabilise the high temperature and better ionic conductor cubic β-phase. This approach has been used to try to obtain a new series of ionic conductors with LAMOX-type structure without molybdenum and presumably better redox stability compared to β-La₂Mo₂O₉. Nanocrystalline materials obtained by a freeze-drying precursor method at 600 °C exhibit mainly the β-La₂W₂O₉ structure, however, the triclinic α-form is stabilised as the firing temperature increases and the crystallite size grows. Only high levels of Ba²⁺ and V⁵⁺ substitutions retained the cubic form at room temperature after firing above 1100 °C. However, these phases are metastable above 700 °C, exhibiting an irreversible transformation to the low temperature triclinic α-phase. The synthesis, structure, phase stability, kinetic of phase transformation and electrical conductivity of these materials have been studied in the present report.     

V2O5-TiO2复合半导体光催化材料结构及光响应性能研究

采用溶胶凝胶法制备了V₂O₅-TiO₂复合半导体材料，通过Raman、XRD及UV-Vis DRS等实验方法研究了V₂O₅与TiO₂复合对材料表面组成、晶体结构以及光响应性能的影响。结果表明：钒加入后优先与TiO₂作用形成较为稳定的金红石型TiVO₄晶相，其中V⁴⁺是促进TiO₂发生相变的关键；随着钒加入量的增加，V₂O₅由表面高分散状态逐渐聚集形成晶相，并释放部分Ti⁴⁺使之形成锐钛矿型TiO₂晶相，使得体相中金红石型TiO₂的含量有所下降；复合后形成的TiVO₄晶相显著提高了材料对可见光的吸收率，并使其吸光域红移至460 nm左右。     

Water-soluble poly(2-(3thienyloxy)ethanesulfonic acid)/V2O5 nanocomposites: synthesis and electrochromic properties

Water-soluble conducting poly(2-(3thienyloxy)ethanesulfonic acid) (PTOESA)/V₂O₅ nanocomposite, (PTOESA)_xV₂O₅, was prepared by simply mixing PTOESA with V₂O₅ wet gel at room temperature. XRD data showed that the interlayer spacings of (PTOESA)_xV₂O₅ films are 14.0±1.5 Å and increased as the polymer content increased. These values are consistent with the insertion of polythiophene chains into the V₂O₅ layer gallery. The formation of alternative layers of PTOESA and V₂O₅ was further supported by depth profile SIMS analyses. Cyclic voltammograms of (PTOESA)_xV₂O₅ film showed two pairs of redox peaks with colors varying from orange, yellowish green, green, to purple blue, depending on the stoichiometry of the nanocomposites. Moreover, a synergetic effect was observed on the electrochromic properties of these nanocomposites. It was found that the optical contrast (ΔOD) of the composites is better than those of PTOESA and V₂O₅ at the film thickness from 150 to 500 nm. The oxidation optical response time of (PTOESA)_xV₂O₅ is independent of the stoichiometry and falls in between those of PTOESA and V₂O₅. At higher polymer content (x>0.5), the reduction optical response time of (PTOESA)_xV₂O₅ is smaller than those of PTOESA and V₂O₅. Variable temperature conductivity data showed that the conductivity of (PTOESA)_xV₂O₅ films increased as temperature increased, characteristic of thermal activated behavior, which was dominated by the interparticle contact resistance. The room-temperature conductivity of water-soluble (PTOESA)_xV₂O₅ films was in between those of PTOESA and V₂O₅ xerogel and higher conductivity was found in the composite with lower polymer content. The anomalous conductivity of (PTOESA)_xV₂O₅ with high PTOESA content may be due to the reason that the higher the polymer content, the bigger the grain size of (PTOESA)_xV₂O₅ film as revealed with scanning electron microscopy and AFM micrographs.     

Structural study of the NaCdVO4-Cd3V2O8 and CdO-V2O5 sections of the ternary system Na2O-CdO-V2O5

The NaCdVO₄-Cd₃V₂O₈ and CdO-V₂O₅ sections of the ternary system Na₂O-CdO-V₂O₅ have been studied and the crystal structures of Cd₃V₂O₈ and Cd₁₈V₈O₃₈ compounds were determined from single-crystal X-ray diffraction data. Cd₃V₂O₈ crystallizes with the maricite-type structure in space group Pnma, a=9.8133(10) Å, b=6.9882(10) Å, c=5.3251(10) Å and Z=4, whereas Cd₁₈V₈O₃₈ crystallizes in space group P1 with a new-type structure, a=8.5761(14), b=8.607(3), c=12.896(2) Å, α=95.64(1), β=102.45(1), γ=108.42(1)° and Z=1. The Cd₃V₂O₈ structure is made up of Cd1O₄ infinite chains of edge-sharing Cd1O₆ octahedra which are parallel to the b direction. The Cd1O₄ chains are linked together by VO₄ tetrahedra and strongly distorted Cd2O₄ tetrahedra. The structure of Cd₁₈V₈O₃₈ is based on an ordered three-dimensional framework of cadmium and vanadium polyhedra that share corners. The distorted CdO₆ octahedra, CdO₅ trigonal bipyramids and CdO₅ square pyramids share corners, edges or faces.     

Field emission of vertically aligned V2O5 nanowires on an ITO surface prepared with gaseous transport

Growing V₂O₅ nanowires (NWs) on a conducting glass substrate combines gaseous transport and pyrolytic deposition of vanadium polyoxometalate anions, and yields vertically aligned vanadium-oxide nanowires. Scanning electron and transmission electron microscopy, selected-area electron diffraction, Raman spectra and powder X-ray analyses indicate that V₂O₅ nanowires as synthesized were single-crystalline and grew anisotropically among direction [010]. NH₂OH·HCl served not only as a reducing agent to produce vanadium polyoxometalate clusters but also as a source of NH₃ gas to facilitate the vapor pyrolysis and deposition. The optical properties of V₂O₅ nanowires exhibit a character dependent on structure. Field emission (FE) measurements show a small turn-on field voltage ~8.3 V/μm, maximum current density 1.8 mA/cm², and a linear Fowler–Nordheim behavior.     

Synthesis, structure and electrical properties of Cu3.21Ti1.16Nb2.63O12 and the CuOx-TiO2-Nb2O5 pseudoternary phase diagram

Subsolidus phase relations in the CuO_x-TiO₂-Nb₂O₅ system were determined at 935 °C. The phase diagram contains one new phase, Cu_3.21Ti_1.16Nb_2.63O₁₂ (CTNO) and one rutile-structured solid solution series, Ti_1−3xCu_xNb_2xO₂: 0<x<0.2335 (35). The crystal structure of CTNO is similar to that of CaCu₃Ti₄O₁₂ (CCTO) with square planar Cu²⁺ but with A site vacancies and a disordered mixture of Cu⁺, Ti⁴⁺ and Nb⁵⁺ on the octahedral sites. It is a modest semiconductor with relative permittivity ∼63 and displays non-Arrhenius conductivity behavior that is essentially temperature-independent at the lowest temperatures.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

V2O5空心球作为高效硫载体用于锂硫电池（英文）

以V2O5空心球作为锂硫电池的正极材料,将其用于存储硫和限制多硫化物的穿梭效应。V2O5空心球的平均直径约为500 nm,为存储硫提供了更多空间并适应硫电极的体积变化。同时,V2O5对多硫化物具有很强的化学吸附性,可以有效地限制多硫化物的穿梭效应。由于中空结构增加了硫的存储,并通过化学键牢固地吸附多硫化物,使该锂硫电池同时具有高容量和良好的稳定性。V2O5/S作为正极的锂硫电池在0.1C倍率时显示出1439 mAh·g-1的高可逆容量,并在1C的倍率下循环300次后的容量约为600 mAh·g-1。     

High-pressure transitions in MgAl2O4 and a new high-pressure phase of Mg2Al2O5

Phase transitions in MgAl₂O₄ were examined at 21-27 GPa and 1400-2500 °C using a multianvil apparatus. A mixture of MgO and Al₂O₃ corundum that are high-pressure dissociation products of MgAl₂O₄ spinel combines into calcium-ferrite type MgAl₂O₄ at 26-27 GPa and 1400-2000 °C. At temperature above 2000 °C at pressure below 25.5 GPa, a mixture of Al₂O₃ corundum and a new phase with Mg₂Al₂O₅ composition is stable. The transition boundary between the two fields has a strongly negative pressure-temperature slope. Structure analysis and Rietveld refinement on the basis of the powder X-ray diffraction profile of the Mg₂Al₂O₅ phase indicated that the phase represented a new structure type with orthorhombic symmetry (Pbam), and the lattice parameters were determined as a=9.3710(6) Å, b=12.1952(6) Å, c=2.7916(2) Å, V=319.03(3) Å³, Z=4. The structure consists of edge-sharing and corner-sharing (Mg, Al)O₆ octahedra, and contains chains of edge-sharing octahedra running along the c-axis. A part of Mg atoms are accommodated in six-coordinated trigonal prism sites in tunnels surrounded by the chains of edge-sharing (Mg, Al)O₆ octahedra. The structure is related with that of ludwigite (Mg, Fe²⁺)₂(Fe³⁺, Al)(BO₃)O₂. The molar volume of the Mg₂Al₂O₅ phase is smaller by 0.18% than sum of molar volumes of 2MgO and Al₂O₃ corundum. High-pressure dissociation to the mixture of corundum-type phase and the phase with ludwigite-related structure has been found only in MgAl₂O₄ among various A²⁺B³⁺₂O₄ compounds.     

Acidic properties of V2O5-WO3/ZrO2 catalysts

The adsorption of pyridine on V₂O₅−WO₃/ZrO₂ has been studied by FTIR. In V₂O₅/ZrO₂ (2 wt.%), the number of both Br?nsted and Lewis acidic sites increased with the addition of WO₃, while in V₂O₅/ZrO₂ (5 wt.%), Br?nsted sites increased and Lewis sites did not change.     

Synthesis, structure and magnetic properties of new vanadate PbCo2V2O8

A new vanadate PbCo₂V₂O₈ was obtained through the study of PbO-CoO-V₂O₅ ternary system. The crystal structure was determined by Rietveld method, indicating that PbCo₂V₂O₈ has a tetragonal structure of space group I41cd with a spiral chain along the c-axis. Magnetic properties of the titled compound were investigated by means of susceptibility, magnetization, and heat capacity measurements. The results show that PbCo₂V₂O₈ is a quasi-one-dimensional canted antiferromagnet with Neel temperature of ∼4 K, being consistent with its crystal structure.     

Preparation and characterization of spherical V2O3 nanopowder

V₂O₃ nanopowder with spherical particles was prepared by reducing pyrolysis of the precursor, (NH₄)₅[(VO)₆(CO₃)₄(OH)₉]·10H₂O, in H₂ atmosphere. The thermolysis process of the precursor in a H₂ flow was investigated by thermogravimetric analysis and differential thermal analysis. The results indicate that pure V₂O₃ forms at 620°C and crystallizes at 730°C. The effects of various reductive pyrolysis conditions on compositions of V₂O₃ products were studied. Scanning electron micrographs show that the particles of the V₂O₃ powder obtained at 650°C for 1 h are spherical about 30 nm in size with more homogeneous distribution. Experiments show that nanopowder has larger adsorption capacity to gases and is more easily reoxidized by air at room temperature than micropowder. Differential scanning calorimetry experiment indicates that the temperature of phase transition of nano-V₂O₃ powder is −119.5°C on cooling or −99.2°C on heating. The transition heats are −12.55 J g⁻¹ on cooling and 11.42 J g⁻¹ on heating, respectively.     

Electrodeposition of mesoporous V2O5 with enhanced lithium-ion intercalation property

Mesoporous vanadium oxide (V₂O₅) thin films were deposited electrochemically onto indium tin oxide-coated glass substrates from an aqueous solution of vanadyl sulfate using CTAB (hexadecyltrimethylammonium bromide) as a templating agent. For comparison, a control sample was electrodeposited without CTAB templating. Transmission electron microscopy and small angle X-ray diffraction indicated the presence of mesoporosity with a well-ordered lamellar phase in the electrodeposited films. The crystallinity of the V₂O₅ thin films was confirmed by X-ray diffraction. Cyclicvoltammetry and chronoamperometry were used to measure electrochemical properties of synthesized films. The mesoporous films prepared with CTAB templating had a much higher capacity and lithium-ion diffusion rate than the non-porous electrode prepared without CTAB templating.     

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO-Bi2O3-Nb2O5-Li2B4O7 glass system

Transparent glasses of various compositions in the system (100−x)Li₂B₄O₇−x(SrO-Bi₂O₃-Nb₂O₅) (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi₂Nb₂O₉ phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple-Didomemenico and Gladstone-Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active.     

Synthesis, crystal structure and nonlinear optical property of Rb3V5O14

The new nonlinear optical crystal Rb₃V₅O₁₄ has been synthesized by solid state reaction and characterized by single-crystal X-ray diffraction, IR and thermogravimetric analysis. The crystal Rb₃V₅O₁₄ crystallizes in the trigonal system with space P31m (No. 157), a=b=8.7134(12) Å, c=5.2807(11) Å and α=90°, β=90°, γ=120°, Z=1, ρ=3.516 g/cm³. It is a layered structure that is very flat and strongly parallel to c. The V₅O₁₄ layer structure consists of corner-linked square and triangular pyramids. The layers are separated by Rb⁺ ions, which fit equally well on the V₅O₁₄ layer. The Kurtz powder SHG measurement, using 1064 nm radiation, showed that the second-harmonic generation efficiency of Rb₃V₅O₁₄ is about two times that of KDP.     

Structure and Ionic Conductivity of Bi6Cr2O15, a New Structure Type Containing (Bi12O14)n Columns and CrO4 Tetrahedra

Powder samples of the Cr⁶⁺-containing compound Bi₆Cr₂O₁₅ were prepared by solid state reaction of Bi₂O₃ and Cr₂O₃ in air at 650°C. The structure was solved and refined using high-resolution neutron powder diffraction data in space group Ccc2, with anisotropic thermal displacement parameters a=12.30184(5), b=19.87492(7), and c=5.88162(2) Å, V=1438.0 ų, and 126 variables to R_F=1.8%. Bi₆Cr₂O₁₅ exhibits a new structure type that contains (Bi₁₂O₁₄)⁸ⁿ⁺_n columns, of the kind previously found only for phases isotypic with Bi₁₃Mo₄VO₃₄. Each column is surrounded by eight CrO²⁻₄ tetrahedra. The ionic conductivity of Bi₆Cr₂O₁₅ was determined by impedance measurements to be 3.5×10⁻⁵ (Ω cm)⁻¹ at 600°C.     

Crystal chemistry and crystallography of the Aurivillius phase Bi5AgNb4O18

Bi₅AgNb₄O₁₈ is a new phase, which was discovered during the phase equilibrium study of the Bi₂O₃-Ag₂O-Nb₂O₅ system. Bi₅AgNb₄O₁₈ was prepared at 750°C and is stable in air up to its melting temperature of 1160.1±5.0°C (standard error of estimate). Results of a Rietveld refinement using neutron powder diffraction confirmed that Bi₅AgNb₄O₁₈ is isostructural with Bi₃TiNbO₉, Bi₅NaNb₄O₁₈, and Bi₅KNb₄O₁₈. The structure was refined in the orthorhombic space group A2₁am, Z=2, and the lattice parameters are a=5.4915(2) Å, b=5.4752(2) Å, c=24.9282(8) Å, and V=749.52(4) Å³. The structure can be described as the m=2 member of the Aurivillius family, (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ (where A=Bi and B=Ag, Nb), which is characterized by perovskite-like (A_m−1B_mO_3m+1)²⁻ slabs regularly interleaved with (Bi₂O₂)²⁺ layers. The octahedral [NbO₆] units are distorted with Nb-O distances ranging from 1.856(4) to 2.161(2) Å and the O-Nb-O angles ranging from 82.6(3)° to 98.5(3)°. These octahedra are tilted about the a- and c-axis by about 10.3° and 12.4°, respectively. Ag was found to substitute exclusively into the Bi-site that is located in the layer between the two distorted [NbO₆] units. Although the Ag substitutes into the Bi-site with the Bi:Ag ratio of 1:1, the existence of a superlattice was not detected using electron diffraction. A comparison of (Bi₂O₂)²⁺(A_m−1Nb_mO_3m+1)²⁻ structures (where A=Ag, Na, and K) revealed a relation between the pervoskite tolerance factor, t, and structural distortion. The reference pattern for Bi₅AgNb₄O₁₈ has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File.     

Electronic parameters of Sr2Nb2O7 and chemical bonding

X-ray photoelectron spectroscopy (XPS) measurements were carried out on a strontium pyroniobate (Sr₂Nb₂O₇) powder sample, which was synthesized using standard solid-state method. The binding energy (BE) differences between the O 1s and cation core levels, Δ(O-Nb)=BE(O 1s)-BE(Nb 3d_5/2) and Δ(O-Sr)=BE(O 1s)-BE(Sr 3d_5/2), were used to characterize the valence electron transfer on the formation of the Nb-O and Sr-O bonds. The chemical bonding effects were considered on the basis of our XPS results for Sr₂Nb₂O₇ and earlier published structural and XPS data for other Sr- or Nb-containing oxide compounds. The new data point for Sr₂Nb₂O₇ is consistent with the previously derived relationship for a set of Nb⁵⁺-niobates that Δ(O-Nb) increases with increasing mean Nb-O bond distance, L(Nb-O). A new empirical relationship between Δ(O-Sr) and L(Sr-O) was also obtained. Interestingly, the correlation between Δ(O-Sr) and L(Sr-O) was found to differ from that between Δ(O-Nb) and L(Nb-O). Possible cause for the difference is discussed.